Editor: When picking a custom color dynamically set a text color with good contrast

[apeatling]

If I set the background color of a group block to predefined colors, the text color inside of the group block is set to a color with an appropriate contrast (as chosen by the theme css classes has-secondary-background)

However, if I set the background color of a group block to a custom color, the text color always switches to dark grey. This means I cannot set a custom dark background color as the text is unreadable with no way to change the color.

Let's see if Gutenberg core would be interested in an enhancement where when picking a custom background color we also dynamically set a text color with good contrast.

[gwwar]

@apeatling I think this might be an enhancement rather than a bug. When a theme preset is picked it applies the more generic class has-x-background-color, which provides a color background and text value. The editor is not setting dynamic values, so when a custom color is picked for background, it doesn't attempt to update the text colors.

[gwwar]

I think it'd still be a nice improvement, but we might want to see if a try PR is possible in Gutenberg since this is a core block.

[glendaviesnz]

I have this working on a branch, with changes to the custom background dynamically setting text color to black or white depending on which provides the best contrast, and also adds a custom text color picker so this can be modified by the user:

I haven't quite got the setting of the custom text color working correctly, should be able to get it sorted and a PR up tomorrow.