Add text color picker so that non-Paragraph children of Group blocks can be correctly colored

[benlk]

In the above screenshot, the Group block has a background color set.

The Paragraph block has a white text color set.

The List block has no color set, and no color settings are available. Instead, it's using the default text color.

I think there are two options here:

1. Put the text color controls on the Group block
2. Add the text color controls to the List block and any other block that may need them.

[benlk]

This is fixed in Gutenberg 7.4, released yesterday: https://make.wordpress.org/core/2020/02/05/whats-new-in-gutenberg-5-february/