Which named colors are available? It is a mystery~

[MostAwesomeDude]

Hi! Making graphs, I noticed that I had two colors, "red" and "orange", and I pondered: Would the color between them be "redorange" or "orangered"? Perhaps "tangerine" or "bloodorange"? It'd be easy to tell if I knew which color standard were being used; my guesses are CSS, matplotlib, W3C, and X11. Dunno which, but we can find out!

This issue's mostly for me; I think that I can fix it by researching and documenting.

[MostAwesomeDude]

Almost not worth documenting separately; it's clearly written in Graphite's documentation here: http://graphite.readthedocs.io/en/latest/render_api.html#bgcolor