Bug 1049198 - Camera/Video should use mark Color layer as [not visible] ...

...when covered by video
This is presumably important to establish a solid color layer, right? I think I tried this and found that it just added a new color layer further down in the layer tree than I expected and did not impact the Thebes layer that we were trying to get rid of.

It seems reasonable to have this here. I'd suggest adding a comment explaining why this is important or at least what it is attempting to do.