Did you everr find anything that works for you?

Procion or other fiber-reactive dyes are the way to go if you want truely vibrant colors (Dharma Trading is my go-to-crew for dying)

if you're stuck with RIT? use half as much water (or twice as much dye) and simmer it on the stove for at least half an hour...or go out and buy an old crock pot for $5, and use that.

Did you dye it using luke warm / not so hot water?