You can apply a weight[0][1] to each of the R, G and B components before computing the distance to get results that approximate doing the distance in Lab color space. The main benefit being that this is a lot cheaper computationally than actually converting to Lab, if you are already working in RGB.

0: https://godsnotwheregodsnot.blogspot.com/2011/09/weighted-eu...

1: https://www.compuphase.com/cmetric.htm