Suggestions for UI enhancements for the next version of this type of thing:
Allow real time modification of the colors (including transparency)
Be able to choose where the colors are (background, border, text, other)
Able to type in or remove domains or maybe even communities and users and set the colors
(Probably too complex but ) have domains be on a selection menu with some indicator of their actual federation status
The latter is because this federation thing is very fluid and what you set this week may not be the best for next. Dare to dream that we could have some federation setting that would automatically determine where each domain is currently and let us know via this kind of thing, vs. having to research or go by word of mouth all the time.