It might not be "just color fixing", but to my eye at least, the results appear similar to if you were to simlpy white balance in lightroom (which doesn't always require a color chart either).
It's clearly much better than that. The problem is that, in a medium like water, light of different wavelengths absorb differently. So the longer distance the light travels through water, the more the effect is, and this effect is different depending on the wavelength. So you can't just open Photoshop and change the color levels of everything in the picture simultaneously. You actually have to know/estimate distances to different objects and make adjustments locally based on that.
