diff --git a/plots/bar-grouped/implementations/python/altair.py b/plots/bar-grouped/implementations/python/altair.py
index 4d76fa6f19..5575016f36 100644
--- a/plots/bar-grouped/implementations/python/altair.py
+++ b/plots/bar-grouped/implementations/python/altair.py
@@ -1,13 +1,32 @@
-""" pyplots.ai
+""" anyplot.ai
 bar-grouped: Grouped Bar Chart
-Library: altair 6.0.0 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-24
+Library: altair 6.1.0 | Python 3.13.13
+Quality: 86/100 | Updated: 2026-05-06
 """
 
-import altair as alt
+import os
+import sys
+
 import pandas as pd
 
 
+# Remove current directory from path to avoid local altair.py shadowing
+script_dir = os.path.dirname(os.path.abspath(__file__))
+sys.path = [p for p in sys.path if p != script_dir and os.path.abspath(p) != script_dir]
+
+import altair as alt  # noqa: E402
+
+
+# Theme tokens (see prompts/default-style-guide.md "Background" + "Theme-adaptive Chrome")
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+
+# Okabe-Ito palette (positions 1→3)
+OKABE_ITO = ["#009E73", "#D55E00", "#0072B2"]
+
 # Data: Quarterly revenue by product line
 data = pd.DataFrame(
     {
@@ -35,25 +54,38 @@
     alt.Chart(data)
     .mark_bar(cornerRadiusTopLeft=3, cornerRadiusTopRight=3)
     .encode(
-        x=alt.X("Quarter:O", title="Quarter", axis=alt.Axis(labelFontSize=18, titleFontSize=22)),
+        x=alt.X(
+            "Quarter:O",
+            title="Quarter",
+            axis=alt.Axis(labelFontSize=18, titleFontSize=22, labelColor=INK_SOFT, titleColor=INK),
+        ),
         xOffset="Product:N",
-        y=alt.Y("Revenue:Q", title="Revenue (thousands USD)", axis=alt.Axis(labelFontSize=18, titleFontSize=22)),
+        y=alt.Y(
+            "Revenue:Q",
+            title="Revenue (thousands USD)",
+            axis=alt.Axis(labelFontSize=18, titleFontSize=22, labelColor=INK_SOFT, titleColor=INK),
+        ),
         color=alt.Color(
             "Product:N",
-            scale=alt.Scale(domain=["Software", "Hardware", "Services"], range=["#306998", "#FFD43B", "#4ECDC4"]),
+            scale=alt.Scale(domain=["Software", "Hardware", "Services"], range=OKABE_ITO),
             legend=alt.Legend(
-                title="Product Line", titleFontSize=20, labelFontSize=18, orient="top-right", direction="vertical"
+                title="Product Line", titleFontSize=20, labelFontSize=18, orient="bottom", direction="horizontal"
             ),
         ),
         tooltip=["Quarter", "Product", "Revenue"],
     )
     .properties(
-        width=1600, height=900, title=alt.Title("bar-grouped · altair · pyplots.ai", fontSize=28, anchor="middle")
+        width=1600,
+        height=900,
+        background=PAGE_BG,
+        title=alt.Title("bar-grouped · altair · anyplot.ai", fontSize=28, anchor="middle"),
     )
-    .configure_axis(gridColor="#E0E0E0", gridOpacity=0.3)
-    .configure_view(strokeWidth=0)
+    .configure_axis(domainColor=INK_SOFT, tickColor=INK_SOFT, gridColor=INK, gridOpacity=0.10)
+    .configure_view(fill=PAGE_BG, stroke=INK_SOFT, strokeWidth=0)
+    .configure_title(color=INK)
+    .configure_legend(fillColor=ELEVATED_BG, strokeColor=INK_SOFT, labelColor=INK_SOFT, titleColor=INK)
 )
 
 # Save as PNG and HTML
-chart.save("plot.png", scale_factor=3.0)
-chart.save("plot.html")
+chart.save(f"plot-{THEME}.png", scale_factor=3.0)
+chart.save(f"plot-{THEME}.html")
diff --git a/plots/bar-grouped/metadata/python/altair.yaml b/plots/bar-grouped/metadata/python/altair.yaml
index 6a601a3d25..bb564ff454 100644
--- a/plots/bar-grouped/metadata/python/altair.yaml
+++ b/plots/bar-grouped/metadata/python/altair.yaml
@@ -1,164 +1,211 @@
 library: altair
+language: python
 specification_id: bar-grouped
 created: '2025-12-24T21:28:44Z'
-updated: '2025-12-24T21:32:11Z'
-generated_by: claude-opus-4-5-20251101
-workflow_run: 20494137794
-issue: 0
-python_version: 3.13.11
-library_version: 6.0.0
-preview_url: https://storage.googleapis.com/anyplot-images/plots/bar-grouped/altair/plot.png
-preview_html: https://storage.googleapis.com/anyplot-images/plots/bar-grouped/altair/plot.html
-quality_score: 92
-impl_tags:
-  dependencies: []
-  techniques:
-  - hover-tooltips
-  - html-export
-  patterns: []
-  dataprep: []
-  styling: []
+updated: '2026-05-06T11:10:02Z'
+generated_by: claude-haiku
+workflow_run: 25431182733
+issue: 1822
+python_version: 3.13.13
+library_version: 6.1.0
+preview_url_light: https://storage.googleapis.com/anyplot-images/plots/bar-grouped/python/altair/plot-light.png
+preview_url_dark: https://storage.googleapis.com/anyplot-images/plots/bar-grouped/python/altair/plot-dark.png
+preview_html_light: https://storage.googleapis.com/anyplot-images/plots/bar-grouped/python/altair/plot-light.html
+preview_html_dark: https://storage.googleapis.com/anyplot-images/plots/bar-grouped/python/altair/plot-dark.html
+quality_score: 86
 review:
   strengths:
-  - Excellent use of Altair declarative xOffset encoding for creating grouped bars
-    without manual position calculation
-  - Clean readable code structure following KISS principles
-  - Colorblind-safe color palette with good visual distinction between product lines
-  - Appropriate font sizes ensure readability at target resolution
-  - Tooltips enhance the interactive HTML version
-  - Realistic business scenario with meaningful quarterly revenue data showing clear
-    trends
+  - Perfect technical execution across all core categories (Visual Quality 30/30,
+    Spec Compliance 15/15, Data Quality 15/15, Code Quality 10/10)
+  - Excellent theme-adaptive implementation with proper use of INK/INK_SOFT tokens
+    in both light and dark renders
+  - Clean, professional grouped bar chart with Okabe-Ito palette correctly applied
+    (green, orange, blue)
+  - Proper data selection and realistic quarterly revenue scenario demonstrating product
+    performance comparison
+  - Idiomatic altair usage with correct encodings, mark types, and configuration methods
+  - All text elements properly sized and readable at full resolution in both themes
+  - Effective use of xOffset for grouped bar positioning with appropriate spacing
+    and clarity
   weaknesses:
-  - Legend placement in top-right overlaps slightly with the plot area; consider orient
-    right outside the plot
-  image_description: 'The plot displays a grouped bar chart showing quarterly revenue
-    by product line. There are 4 quarters (Q1-Q4) on the x-axis, each with 3 side-by-side
-    bars representing Software (dark blue #306998), Hardware (yellow #FFD43B), and
-    Services (teal #4ECDC4). The y-axis shows "Revenue (thousands USD)" ranging from
-    0 to 180. The title "bar-grouped · altair · pyplots.ai" appears at the top center.
-    A legend labeled "Product Line" is positioned in the top-right corner. The bars
-    have subtle rounded corners at the top. Software consistently has the highest
-    revenue across all quarters (120→145→132→168), Hardware is mid-range (85→78→92→105),
-    and Services is lowest but growing (45→52→68→75). The grid is very subtle with
-    low opacity.'
+  - 'DE-01 and DE-02 could be elevated: consider more sophisticated design elements
+    like custom typography hierarchy, visual emphasis through color intensity variation,
+    or layered visual storytelling beyond the default grouped bar structure'
+  - 'LM-02 (Distinctive Features) is minimal at 2/5: could leverage altair''s interactive
+    capabilities such as selection, interactive pan/zoom, or brushing to showcase
+    library-specific strengths'
+  - 'DE-03 (Data Storytelling) relies on natural structure rather than intentional
+    emphasis: consider adding color dominance patterns, size variation, or strategic
+    annotation to guide viewer attention more forcefully'
+  image_description: |-
+    Light render (plot-light.png):
+      Background: Warm off-white #FAF8F1 with subtle grid lines at 10% opacity. Clean, minimal aesthetic.
+      Chrome: Title "bar-grouped · altair · anyplot.ai" in dark (#1A1A17) at 28px, clearly visible. X-axis label "Quarter" and Y-axis label "Revenue (thousands USD)" in dark text at 22px, fully readable. Tick labels (Q1-Q4, 0-180) at 18px in secondary color (#4A4A44), legible. Legend "Product Line" with colored squares (Software/Hardware/Services) at bottom, dark text on light background.
+      Data: Three product lines rendered as grouped bars with Okabe-Ito colors: Software=#009E73 (green), Hardware=#D55E00 (orange), Services=#0072B2 (blue). Bars have subtle rounded corners. Spacing between groups is appropriate for visual separation. Data density is ideal (4 quarters × 3 products = 12 bars total).
+      Legibility verdict: PASS - All text is readable. No text-on-text collisions. Strong contrast between chrome and background.
+
+    Dark render (plot-dark.png):
+      Background: Warm near-black #1A1A17 with subtle grid lines. Matches light theme aesthetic perfectly.
+      Chrome: Title in light color (#F0EFE8) at 28px, clearly visible against dark background. Axis labels in light text at 22px, fully readable. Tick labels in lighter secondary color (#B8B7B0) at 18px, legible. Legend maintains dark background with light text, proper contrast.
+      Data: The three Okabe-Ito colors (#009E73, #D55E00, #0072B2) are IDENTICAL to light render, ensuring brand consistency. Bars are clearly visible and distinguishable from dark background. Rounded corners maintain visual identity.
+      Legibility verdict: PASS - No dark-on-dark issues. All elements properly adapted for dark theme. Brand green (#009E73) is vibrant and distinct. Both renders are theme-correct.
+
+    Summary: Both renders pass legibility checks. Chrome adapts properly between themes (only background/text colors flip). Data colors remain constant. Professional, readable visualization in both light and dark contexts.
   criteria_checklist:
     visual_quality:
-      score: 37
-      max: 40
+      score: 30
+      max: 30
       items:
       - id: VQ-01
         name: Text Legibility
-        score: 10
-        max: 10
+        score: 8
+        max: 8
         passed: true
-        comment: Title at 28pt, axis labels at 22pt, tick labels at 18pt - all clearly
-          readable
+        comment: All text readable at full resolution in both themes. Title 28px,
+          axis labels 22px, tick labels 18px. Proper use of INK and INK_SOFT tokens
+          for light/dark themes.
       - id: VQ-02
         name: No Overlap
-        score: 8
-        max: 8
+        score: 6
+        max: 6
         passed: true
-        comment: No overlapping text elements anywhere
+        comment: Bars properly spaced with xOffset encoding. No text collisions. Legend
+          items well-separated. Clear visual hierarchy.
       - id: VQ-03
         name: Element Visibility
-        score: 8
-        max: 8
+        score: 6
+        max: 6
         passed: true
-        comment: Bars are well-sized with good spacing, xOffset creates clear grouped
-          separation
+        comment: All 12 bars (3 products × 4 quarters) clearly visible. Rounded corners
+          provide subtle definition. Data density appropriate for canvas.
       - id: VQ-04
         name: Color Accessibility
-        score: 5
-        max: 5
+        score: 2
+        max: 2
         passed: true
-        comment: Blue, yellow, and teal are colorblind-safe (no red-green issues)
+        comment: Okabe-Ito palette inherently CVD-safe. Adequate contrast in both
+          themes. Three colors are distinctly differentiable.
       - id: VQ-05
-        name: Layout Balance
+        name: Layout & Canvas
         score: 4
-        max: 5
+        max: 4
         passed: true
-        comment: Good proportions, though legend in top-right slightly overlaps grid
-          area
+        comment: Canvas 1600×900 with scale_factor=3.0 = 4800×2700px (correct). Good
+          proportions. Margins and padding appropriate. No elements cut off.
       - id: VQ-06
-        name: Axis Labels
+        name: Axis Labels & Title
         score: 2
         max: 2
         passed: true
-        comment: Y-axis has descriptive label with units "Revenue (thousands USD)",
-          X-axis labeled "Quarter"
+        comment: 'X-axis: ''Quarter'' (descriptive). Y-axis: ''Revenue (thousands
+          USD)'' (includes units). Title: ''bar-grouped · altair · anyplot.ai'' (matches
+          spec format).'
       - id: VQ-07
-        name: Grid & Legend
-        score: 0
+        name: Palette Compliance
+        score: 2
         max: 2
         passed: true
-        comment: Grid is appropriately subtle (alpha 0.3), but legend overlaps the
-          data area slightly
+        comment: 'Software=#009E73 (Okabe-Ito pos 1). Hardware=#D55E00 (pos 2). Services=#0072B2
+          (pos 3). Plot backgrounds #FAF8F1 (light) and #1A1A17 (dark). No theme-adaptation
+          failures.'
+    design_excellence:
+      score: 10
+      max: 20
+      items:
+      - id: DE-01
+        name: Aesthetic Sophistication
+        score: 4
+        max: 8
+        passed: false
+        comment: 'Clean professional design but uses default styling patterns. Okabe-Ito
+          palette (not custom). Rounded bar corners show subtle thought. No dramatic
+          visual hierarchy or focal point creation. Score: default 4 (could be higher
+          with custom typography, color intensity variation, or layered visual emphasis).'
+      - id: DE-02
+        name: Visual Refinement
+        score: 3
+        max: 6
+        passed: false
+        comment: 'Grid configured with opacity=0.10 for subtlety. Legend background
+          uses ELEVATED_BG for separation. Whitespace adequate. Rounded corners show
+          refinement touch. No spines explicitly removed but design is clean. Score:
+          3 (modest customization, not highly refined).'
+      - id: DE-03
+        name: Data Storytelling
+        score: 3
+        max: 6
+        passed: false
+        comment: 'Grouped bar arrangement naturally guides product comparison within
+          quarters. Ascending revenue pattern visible across Q1-Q4. Color consistency
+          creates narrative. Software (green) shows clear dominance across all quarters.
+          No additional visual hierarchy or emphasis techniques applied. Score: 3
+          (good natural storytelling from structure, but could be more intentional).'
     spec_compliance:
-      score: 25
-      max: 25
+      score: 15
+      max: 15
       items:
       - id: SC-01
         name: Plot Type
-        score: 8
-        max: 8
-        passed: true
-        comment: Correct grouped bar chart with side-by-side bars per category
-      - id: SC-02
-        name: Data Mapping
         score: 5
         max: 5
         passed: true
-        comment: Quarter on X, Revenue on Y, Product as grouping variable
-      - id: SC-03
+        comment: Correct grouped bar chart. Uses xOffset encoding for proper side-by-side
+          positioning. Chart type implementation is accurate.
+      - id: SC-02
         name: Required Features
-        score: 5
-        max: 5
+        score: 4
+        max: 4
         passed: true
-        comment: Distinct colors, clear legend, consistent bar widths, good spacing
-          between groups
-      - id: SC-04
-        name: Data Range
+        comment: 3 product lines displayed side-by-side for each quarter. Clear legend
+          with product names. Proper axis labels and title. Tooltips enabled for data
+          exploration.
+      - id: SC-03
+        name: Data Mapping
         score: 3
         max: 3
         passed: true
-        comment: Y-axis shows full range 0-180, all data visible
-      - id: SC-05
-        name: Legend Accuracy
-        score: 2
-        max: 2
-        passed: true
-        comment: Legend correctly labels Software, Hardware, Services
-      - id: SC-06
-        name: Title Format
-        score: 2
-        max: 2
+        comment: 'X: Quarter (categorical, ordinal). Y: Revenue (quantitative, 0-180
+          range). Color: Product (categorical, Okabe-Ito). All data dimensions properly
+          mapped.'
+      - id: SC-04
+        name: Title & Legend
+        score: 3
+        max: 3
         passed: true
-        comment: Uses correct format "bar-grouped · altair · pyplots.ai"
+        comment: 'Title format matches spec: ''bar-grouped · altair · anyplot.ai''.
+          Legend labeled ''Product Line'' with correct entries. Bottom placement is
+          standard and readable.'
     data_quality:
-      score: 20
-      max: 20
+      score: 15
+      max: 15
       items:
       - id: DQ-01
         name: Feature Coverage
-        score: 8
-        max: 8
+        score: 6
+        max: 6
         passed: true
-        comment: Shows variation across quarters and between products, clear trends
-          visible
+        comment: Demonstrates core grouped bar feature with 3 product lines across
+          4 quarters. Shows product differentiation and quarterly trends. All expected
+          chart elements present.
       - id: DQ-02
         name: Realistic Context
-        score: 7
-        max: 7
+        score: 5
+        max: 5
         passed: true
-        comment: Quarterly revenue by product line is a real business scenario
+        comment: Business scenario (quarterly revenue by product line) is realistic
+          and relatable. Revenue values (45-168k USD) are sensible. Product categories
+          (Software, Hardware, Services) are appropriate. Data relationships are authentic
+          and neutral.
       - id: DQ-03
         name: Appropriate Scale
-        score: 5
-        max: 5
+        score: 4
+        max: 4
         passed: true
-        comment: Revenue values 45-168 thousands USD are realistic for product lines
+        comment: Y-axis range (0-180) is proportional to data spread. No wasted canvas
+          or excessive compression. Values are well-distributed across the visual
+          range for clear comparison.
     code_quality:
-      score: 7
+      score: 10
       max: 10
       items:
       - id: CQ-01
@@ -166,42 +213,72 @@ review:
         score: 3
         max: 3
         passed: true
-        comment: Simple imports → data → chart → save structure, no functions/classes
+        comment: Direct DataFrame creation and chart building. No unnecessary functions
+          or classes. Straightforward, readable code structure.
       - id: CQ-02
         name: Reproducibility
-        score: 0
-        max: 3
-        passed: false
-        comment: No random data, but data is deterministic (hardcoded) - however,
-          the code does not use np.random.seed as there's no random data
+        score: 2
+        max: 2
+        passed: true
+        comment: Data is hardcoded deterministically. No randomness or external dependencies.
+          Output is consistent across runs.
       - id: CQ-03
         name: Clean Imports
         score: 2
         max: 2
         passed: true
-        comment: Only altair and pandas imported, both used
+        comment: 'Only necessary imports: os, sys, pandas, altair. sys path manipulation
+          is needed to avoid shadowing. No extraneous imports.'
       - id: CQ-04
-        name: No Deprecated API
-        score: 1
-        max: 1
+        name: Code Elegance
+        score: 2
+        max: 2
         passed: true
-        comment: Uses current Altair API
+        comment: Uses appropriate altair patterns (mark_bar, encode, properties, configure).
+          No fake interactivity. Theme-adaptive logic is clean and clear.
       - id: CQ-05
-        name: Output Correct
+        name: Output & API
         score: 1
         max: 1
         passed: true
-        comment: Saves as plot.png and plot.html
-    library_features:
-      score: 3
-      max: 5
+        comment: Correctly saves as f'plot-{THEME}.png' and f'plot-{THEME}.html'.
+          Uses current Altair 6.1.0 API. scale_factor=3.0 is appropriate.
+    library_mastery:
+      score: 6
+      max: 10
       items:
-      - id: LF-01
-        name: Uses distinctive library features
-        score: 3
+      - id: LM-01
+        name: Idiomatic Usage
+        score: 4
         max: 5
-        passed: true
-        comment: Uses xOffset for grouping (Altair-specific), cornerRadius for styling,
-          tooltips for interactivity, declarative encoding. Could have added selection/interactivity
-          features.
+        passed: false
+        comment: Uses altair's recommended grammar of graphics. Proper mark_bar()
+          and encoding patterns. xOffset for grouping is idiomatic altair technique.
+          Proper configuration methods. Missing more advanced interactive patterns
+          (interactive(), selection()) for full mastery.
+      - id: LM-02
+        name: Distinctive Features
+        score: 2
+        max: 5
+        passed: false
+        comment: Uses basic tooltips and color encoding (standard features). Rounded
+          corners show attention to detail but are minimal. Could leverage altair's
+          interactive capabilities (selection, pan/zoom) or more complex encodings
+          for distinctiveness.
+    score_caps_applied: []
   verdict: APPROVED
+impl_tags:
+  dependencies:
+  - pandas
+  techniques:
+  - grouped-bars
+  - color-encoding
+  - tooltips
+  patterns:
+  - data-generation
+  - theme-adaptation
+  dataprep: []
+  styling:
+  - rounded-corners
+  - theme-adaptive-chrome
+  - publication-ready