There is no option to change the color when the onPress is null

Hi, 

I need to set a "disabled" color in some cases, and I noticed that there is no option to do it currently.
I noticed that when I am setting the "onPressed" to null, the background color of the button changes, but there is no way to change it to what I need.

My question is if there is an option to do it.
If not, can you please add this feature to the next release?

Thanks!