You said, "As Nick has explained before, MOC normalizes it's images where the brightest pixel is registered as white and the darkest as black. This is why things that aren't necessarily black as seen by the eye look VERY dark in MOC images."

And I have seen this (craters that are black dots.)

This is probably the case for the blackest parts of these gullies. But do you know what that means? They are the darkest part of this picture. Perhaps they are not pitch black, but they are the darkest part of the picture. This, along with the other slightly dark gullies mean some kind of dark material is in them. It can not be a shadow, not at 1:30 pm on a summer afternoon.