This was an email from my friend Jay this week:

I was posed with the question the other day if I had a RGB to Gel
conversion chart, and I don't and can't seem to find one on the
internet. I was wondering if anyone has one, or is everyone having to
spend the time trying to mix the colors to get the initial color
groups on colorblazes and whatnot. I have tons of CMY charts, just
not RGB. Let me know if you have one.

Jay

And my response:

Jay, this is a black art! The problem is that with LEDs the intensity
of the light is inherently mashed up with the color values. ie
Intensity goes away as an independant parameter. Because of this you
will find that you will have to mix everything anyway as there will be
little difference in your results for two gel colors that are related
in hue but differ in saturation. Good luck, sorry to not have the
correct incantation for you.