Oh I didn't know you could list values! Nice!
For the colours I was thinking about plotting specifically (although I guess customising UI colours could be nice too), where you would specify a colour attribute per line, before (or after?) an expression to evaluate.
I'm trying to avoid too much "styling control" in the code itself, since it's not really designed as a "picture maker" and I don't want to burden the language syntax, but I've considered stuff like @color(255,128,64) and things of that nature as optional "style comments". I think the primary colorizing would come from a global "settings" menu though, so I'd just allow setting the entire app's color scheme (including the colors for each plotted graph, up to 16 or something). It's not that I don't want it to be used for making pictures, it's just that it's a deep rabbit hole of scope, so I need some kind of self imposed guardrails :P So at the moment it's something like "customizing colors to your liking makes sense, but customizing colors and styles for a perfect diagram to use elsewhere" probably doesn't make sense.