Upgrade: Bump d3-color and vega-embed

Bumps [d3-color](https://github.com/d3/d3-color) to 3.1.0 and updates ancestor dependency [vega-embed](https://github.com/vega/vega-embed). These dependencies need to be updated together.


Updates `d3-color` from 1.4.1 to 3.1.0
- [Release notes](https://github.com/d3/d3-color/releases)
- [Commits](d3/d3-color@v1.4.1...v3.1.0)

Updates `vega-embed` from 3.14.0 to 6.21.0
- [Release notes](https://github.com/vega/vega-embed/releases)
- [Changelog](https://github.com/vega/vega-embed/blob/v6.21.0/CHANGELOG.md)
- [Commits](vega/vega-embed@v3.14.0...v6.21.0)

---
updated-dependencies:
- dependency-name: d3-color
  dependency-type: indirect
- dependency-name: vega-embed
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]