I have a very similar problem with my OSSC using a Dreamcast via VGA. Everything has been working fine until this evening when I discovered the white colours are now all cyan looking and the picture has started to flicker a bit. I have done all the usual things; replaced all cables, directly hooked up VGA to display and capture card, tried a second Dreamcast, etc. I have flashed new/old firmware and reset all OSSC setting. All without any success.
Is it possible to RMA this one too please? It was purchased last November, I have purchase order number I can forward if required with additional details.