Thanks to Rick I was able to fix this UI issue. If you are colorblind and having issues with the "traffic lights" in R21 I went ahead and brought up the contrast and brightened the green ones (almost yellow-ing it... i think, haha). And I switched the Red ones to a very visible blue, so hopefully this is night and day for you, as it is for me now. Replace it where Rick has stated above.
It's too big to attach, so here's a link:
https://drive.google.com/file/d/13MirZgsHipuDNg9Bx9JV2wmThkRp1366/view?usp=sharing
As a side note, I'd plead that more UI designers keep in mind that red green colorblindness is actually relatively common, and by comparison yellow-blue is much rarer, so I wish the defaults would switch over (same for actual traffic lights, too). This is an issue in countless programs and its ironic its not considered more in graphics applications, at least as a checkbox in the preferences. I'm also left-handed (go figure), and there is much more support for toggling a feature for that in drawing apps, for example.
Thanks Rick!