I've only skimmed the paper, but it's more complicated than that. There's both an light attenuation effect (the "blue shift" you're talking about), as well as a separate back-scatter effect, which use different coefficients based on depth. It seems to me that the hard part is figuring out a function to color correct based on both these factors for a large range of depths using a limited number of reference points (as well as getting an accurate depth map, of course).