From the Super Mario Wiki
Rainbow Tap-Taps are colorful variants of Tap-Taps that appear in Yoshi Topsy-Turvy. They are found during the second phase of the battle against Bowser. Whenever Bowser jumps or is hit by a bomb, he slams against the ground, causing three Rainbow Tap-Taps to fall from above. They roll along the ground, and go in the direction that the player tilts the Game Boy Advance. They cause three points of damage to Yoshi upon contact with him.