I was trying out this extension flarum-ext-colorful-borders by @clarkwinkelmann
It still works, but i'd like to be able to set default parameters according to user groups. So I could set a default post background color, border, text color, etc.. for each individual user group. All mods could have a green border, for example.
I'm willing to make a donation to anyone who can modify the extension with this possibility, or make a new extension, that's up to you how you'd want to achieve this.
Name your price/dono request.