I have looked and seen some that are deleted or no longer available. I remember one that you used to have edit a bunch of templates but can't seem to find that anywhere.
It's because it was moved to User groups' (admin.php?user-groups/ Username CSS.
CSS:
color: green;
Will get you:
Unfortunately, it doesn't apply to tags. But, that can also be a good thing with styles varying in colors, and even style variants. Though, if tags came with a class other than username (such as usergroup or another identifier), it'd be easy to implement. It still might be, but I couldn't figure it out.
But, you still have this problem on dark (as you're limited to CSS and not LESS in User groups):
So you'll need to know the class that user group made (inspect). In this case, it's username--style3 where 3 represents the user group (3 = Administrative)
2.2 so wouldn't account for style variations (light/dark mode) as seen above (possibly), but something to try.
I don't like relying on add ons as it's harder to maintain functionality when can be as simple as a style edit. What happens when 2.4 comes out? The style will likely work, whereas the add on might have breaking functionality, especially if you do a PHP update or something. That said, it is MIT, so someone could update it and repost it for it to function with 2.3 style variations, if it doesn't already.