how do I sort dictionaries by value then by key?

What is the correct way to sort colors when calculating a median value?

• Unlike with grayscale values there are many ways how to sort a set of colors: luminance, hue, saturation etc. The common way is probably to sort the rgb, yuv or lab components separately and recombine them, but then the resulting color is very likely not in the original set. And sorting them numerically (24 bit rgb values for example) somehow doesn't feel correct either.

• Answer:

  If you are after the central tendency of a set of colors and want to pick one of the set as its representative, I'd compute all pairwise distances in the set and pick the color whose sum of pairwise distances is the smallest (this is the same as picking the color with the lowest mean distance to all other colors). To make the distances more visually meaningful I would use a color space like CIE LAB (or, even better, CIE CAM02).