A working version of the mixer. Hopefully, this will work fine for you too.
It mixes correctly almost all colors. Do not be surprised that yellow and blue give gray instead of green: just "correct" them so that they're less "pure".
That's an obvious point, since in real paints, yellow and blue give green just because they're not pure. The same with other mixtures. I'll change the basic palette with a more realistic one soon.

This commit disable the whole illuminant-reflectance implementation, because it's not finished and it doesn't work as good as I want to. So the mixer uses a more basic "RGB/KS" color space, that uses RGB values as reflectances and then convert it to Kubelka Munk without any extra calculation. It's a pretty good approach until I finish the "real thing" (tm).

I removed (definitively) gmm matrices and std::vectors. The first because I do not need the features of gmm, the second because they're too slow (once I removed them, my mixer started to be smoothly fast again).
The mixer (temporarly) doesn't depend on glpk (GNU Linear Programming Kit), until I reimplement the illuminant-reflectance color spaces.

So... enjoy something quite interesting, finally! :-)