Glow 'n Show, sparkle, twinkle eye, and rainbow
AT THE SAME TIME.
WOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!
Twinkle-Eye ponies were technically Rainbow ponies already just with unique color combinations. Quackers in fact had the rainbow colors in reverse.
Well, several of them had rainbow hair, but I would say most of them, like Galaxy and Fizzy, that they simply had multi-colored hair. For me, you have to have colors which contrast more starkly to call it rainbow hair.