GPU Gems 2 - Using Lookup Tables to Accelerate Color Transforms
You must use a scale + offset when doing a color cube or similar lookup, you will lose a LOT of precision otherwise since the maps are so small!!!!
Almost all perceptually significant color values are in the lowest cells (dark end of the gamut). You can use a pair of 1D shaper LUTs wrapping around the tex3D to take care of this
Consider Colour Correction Curves instead of LUTs: you can have multiple curves and blend the control points together. Upload a new matrix. Power vector (r^3, r^2, r,1) dotted with the matrix row = new colour.
And its fast as hell.