### Any ideas on the best color difference or distance approximation?

Currently, a standard way of comparing colors is using "Delta E" metric in CIELab [Color-difference] which is based on Euclidean distance in CIELab color space.

However, for certain applications using the distance metric intensively "Delta E" metric could be a bit slow (e.g. RGB2Lab conversion is necessary, floating point operations ~~an ~~can be costly, etc.).

Is there a "good enough approximation" of color difference or distance?

Ex.