It's possible I'm misunderstanding the role of the Interop project, but I was hoping that the Interop team could discuss the inconsistencies with browser vendors and figure out if it's possible to have a way forward. As far as I can tell, the specification is pretty solid.
There are already plenty of tests too. Scrolling through css-color-4 you'll see some of the inconsistencies in test results, although there could probably be tests for more scenarios? For example, the system-color-consistency test does not cover all system colors.
Spun out from a comment by mayank99 who said: