Warn if the user attempts something like plot.project("fill", "red")

(but the function executes unchanged)

I'm OK if you guys want to hold off on this one.
since this variable is exported, we should treat it with static styling like

COMMON_COLORS

Also, I'm not certain on the location of this variable.  My first instinct is colors.ts but one can argue that colors.ts is strictly for plottable's own colors.  Your call on this.