Add option to specify colors for point colorer as array of objects containing r,g,b, and opacity

[joshua-gould]

This makes plotting lots of points significantly faster because colors do not have to be parsed

[cannoneyed]

Yeah, this is a real annoying pain point - in fact, I tried making a little system for this but wound up getting frustrated by some of the ways we handled colors internally (hint, it's all very tied to THREE)... anyway, I think this is worth revisiting.