I get great color blends form 650,532, and 473, all around 100mW.
The problem isn't with the hardware (ok, we do need analog modulation on R,G&B) and not as much with the software(as long as it supports blending) as with most people's tendencies to use primary colors. `We' think in terms of R, G and B - it's technology centered thinking as opposed to artistic thinking. That makes sense since most of us built the projectors ourselves so a technological approach is expected. Now `we' need to become artists
So I don't think that having color cards etc is going to help much. A great way to tackle this 'problem' is by what has already been started: posting the true artist's work and getting inspired by it. The colors are already in the projectors, just need to find them. Try making non-primary color frames, demand from yourself to make blended color frames only. Blended colors are brighter to begin with anyway Combine blue and red to get colors that are not in the rainbow!
E.g. , I could not imagine how to get brown light before trying - but it can be done.