[ chu chu! ]

According to color theory, the complementary color to Orange is Blue, so...

[ bottoms up. ]

So, in my completely unsolicited opinion, it would be the most logical choice, as we haven't started with Red, anyway, and I'm certain most others would be continuing on the Red through Purple progression, as that was the order in which they were presented and rainbows are aesthetically pleasing, also [ this goes on until she's stopped ]