I like to use upper case letters in my css color values. To me, it just looks better, and makes it easier to tell if there's a missing or extra digit. Whatever... To each his own, right? Especially since CSS doesn't care.
Well, after tearing my hair out for three hours last night, I finally figured out what was causing the totally spurious behavior of my theme's color module integration...
The Color Module is intolerant of upper case letters. It reads #45C690 as #000000, and proceeds from there. So you basically get kind of a dark mode thing going for all your color configurations, and it stays that way until you save back to your default.
This is just a heads-up for anyone who might be experiencing this issue.