Don't hang your clothes out here
As to the amazing bright spots.
I cast my vote for bleach. As in sun-bleach. If you have a sublimation going on continuously for eons, then the stuff that get's kicked off is anything that can absorb a photon vs reflecting it.
Hence the high albedo for the moon. The dark molecules absorbed energy until they got hit with enough to kick them into a slightly different position. This is a natural selection process that inevitably results in bright spots where the sun shines, while no doubt there is a higher relative concentration of dark molecules in nearby areas that tend to be in the shadows. Hence the high contrast. An atmosphere tends to smother the process with its own noise, but a slight atmosphere might actually facilitate the process. Think about the days of hanging clothes out in the sun on a clothes line, vs using a dryer. Remember how sun-faded those clothes became after a hundred hours or so of sun drying?
Once the process has started, given a certain amount of relatively reflective material in the mix, it tends to spread like a cancer, with the higher concentrations of reflective molecules driving out the dark molecules. Just like if you put a dark object in a room, you can measure the light eating effect for the entire room. Photons that would otherwise bounce all over until finally being absorbed are quickly eaten by the dark surface. Rooms with lots of dark surfaces require a lot more light energy for the same overall brightness. Of course, the process also works better with light-weight atoms, such as hydrogen and oxygen and carbon. Heavier molecules are better suited to absorb photons without getting kicked around.
Thus perhaps the root cause of the spots is the outjetting of H2O that has been noted for some time. The bright H2O crystals have their own self-segregation, like patterns replicating in "Life." Those that land near darker areas tend to re-sublimate due to the heat output of the dark material and then re-solidify at random until they find a secure spot away from the heat emissions of dark material. Order from chaos. Goodbye, entropy?
The big question is, of course, what exactly are those water plumes as well the bright spots made of? Likely not pure H2O, altho water is nice for various purposes. Given the possible very long spans of time involved, crystal forms may have evolved to rare isomeric geometries - think ICE9 in "Cat's Cradle." Answers may surprise. Next cookie, please...
What an interesting week. First, the bright spots on Ceres; then, the re-estimation of planetary likelihood in general to an expected approximation of at least one planet per star, casting the Fermi Paradox in ever stronger significance.