How to Change CSS Colors from Custom Plugin Settings Page

I have a custom WordPress plugin with a variety of settings that I use across multiple websites. I also use a few of the same 3rd party plugins across all of those pages. I would like to be able to stylize them the same way, but with different colors. While I could add CSS to every site, it is difficult for some of our non-techy admins to go through the CSS and change the hex codes on the correct classes. I am trying to figure out the best way to do this. Here is what I’ve looked into so far: