Because yes, I use GTK V3 in #gjs to output this information. It's the only viable way. But Gtk V4 has removed the access to the context. That's crazy.
And if you're not aware about the problem, there are plenty of developers who ask this on StackOverflow, reddit... The general answer is "we changed this because we do better things now". Better ? That was a pain to find colors, now it's impossible!