On: How to implement search-by-color when all you have...

[julian37]

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