It is the same as the original Krabby Patty, except the patty meat is in the color of a rainbow: pink, violet, indigo, green, yellow, orange, and red.
Role in short
SpongeBob makes the Rainbowger and attempts to serve it to the customers, commenting that it will bring the whole world together. However, Plankton arrives and takes away the patty's color with his color nullifier. He overloads it and starts shooting random colors, coloring people random colors.
Its name is a combination of the words "rainbow" and "burger."
Despite not being a color of the rainbow, the burger has the color pink in its patty.