Just in case anyone else misses the point, what I meant was that /echo [0-15] would use the colour for that index set in the box that opens when you hit ctrl+k, but anything above 15 would refer to the RGB value of a colour.
/echo 37463 -a t would be valid, for example.
As for it being limited, it will let you locally use any colour in the spectrum. I don't actually think it can get any better than that :p
