Yeah, rainbows! I could have sworn that this would be an even bigger Maus face that the two smaller ones were going on. It would have made a great reveal! You forgot orange again! That's still my favorite color! This moves pretty fast.
At first, I thought this would be a reference to MLP. I now realize that MLP (FIM) did not even exist at the time of this. I'm just so used to seeing that everywhere. I associate rainbows with those guys. The colors are really nice.