The Rainbowdians are unstabilized colors of the rainbow. Baby prematurely opened her gift from Love before the colors had time to properly mold together. Initially she met "Yellow" who immediately befriended her and they ran off to celebrate their birthday. After they leave, the rest of the colors escaped and covered the lounge in multiple colors. Love mentions that, if the Rainbowdians aren't brought back together, color pandemonium could ensue.
Blue, Orange and Green argued over the color of the ocean while Indigo and Violet argued over which one was prettier. Red was caught painting all the traffic stops red.
At the end of the episode, HJ5 was able to gather all the Rainbowdians and, using the acceleration of the carnival ride, were able to get the colors to morph together into a rainbow.