You'll get better results using a perceptually uniform color space [1] CIE76 is not ideal but would let you continue to use CUBE. You could consider doing a f

You'll get better results using a perceptually uniform color space [1] CIE76 is not ideal but would let you continue to use CUBE. You could consider doing a first pass with CIE76 and then sort by something more accurate in a second pass. [1] https://en.wikipedia.org/wiki/Color_difference https://en.wikipedia.org/wiki/Color_difference