Yeah, I think Stone Age by Gowin does the same thing too. And I got one of the Yong Yong Digimon games to do it when I was messing around with cheat codes.. it actually booted into the same red/blue/green palette Sonic 7 uses for its intro. I've also seen it in a Yong Yong game on a real cart, for that matter. In fact I've even seen it in Pokemon Gold when I was trying to hack it and I screwed up, so it's not something that only happens in unlicensed games. I think it happens when a game is running on a GBC (or emu in GBC mode) but it resets and for some reason thinks its running on a mono GB, so it just uses some weird default palettes. In the Yong Yong games it makes the music speed up too, presumably because the GBC processor is faster and it messes up the timing of their sound engine.