Good idea.
Keep in mind that 'too many settings just confuses users'.
I used 5 ( They are here: medialog.subskins/medialog/subskins/skins/subskins_colorschemes at master · espenmn/medialog.subskins · GitHub )
I used to 'work around this by using percentages of the colors.
I don't think that is possible with 'css-variables' (but is in some of the others, I think.... or it can be done in a browser view (as I did back in the days)…)
I have quite a few CSS files (and some rules.xml) we could use, but I need help from someone with good diff knowledge to 'reverse engineer' the CSS to LESS or something else...