The graphs can use the color names recognized by the major browsers,
plus transparent to not draw anything at all. You can specify the colors as
red-green-blue triplets, in any of the ways
that CSS recognizes: #bc5,
#abcdef, rgb(100,255,100),
or rgb(50%, 75%, 40%).
rgba colors are also supported to allow for semi-transparent colors. If anyone is interested in hsl colors I can add those as well.