note: bottom-right is the seed number which would overlay over the image.

Power users would love this kind of feature. Very useful info can be conveyed without any waste of real-estate.

I think this would be useful for everyone really, including beginners who would eventually just pick up on the colour coding over time. If it's not understood then it will just be random pretty colours to someone, so it's not any detraction.

With this system it doesn't really matter what the image actually is. It would be handy even to be able to have this on top of uploaded images.

This could be a global toggle in the preferences or default behaviour.