Not a bad idea, but at least one of the videos seems like it's taken from a doorway to a small balcony, and sticky tape on window wouldn't seem to be affected too much by clouds moving around it so that it changes from blurry to clear and partially occluded to more exposed.

My far-out idea is that if it is some sort of human developed thermoptic camouflage, it's not perfect and the dark area is the physical outline of the craft as physical clouds buffet against it.