There is no doubt that the Flat UI was highly inspired by LayerVault, but c'mon, you can't restrict a certain style or color pallete from being used.

It's true that all these flat UI themes are really similar, so It's really interesting how this will turn out and will the Flat UI repo will be brought back.

Google uses the same:

http://i.imgur.com/qJXJUaH.png

It's impossible to pick a green in a tetradic scheme and not get a red, orange and blue to match it.

However in order to win an infringement claim you'd have to show that they constituted a substantial part of a work and that the colours were copied and not derived from a third party source or coincidentally the same. The usual civil law test is the balance of probabilities.

I think a more likely claim is that the matching colour scheme were a trademark infringement, an unlicensed use of trade dress (jurisdiction dependent of course). AFAIK DMCA takedown notices don't work for trademark infringement though?