These transparent fish turn rainbow with white light. ... When the fish contracts and relaxes its muscles to swim, the sarcomeres slightly change in length, causing a shifting rainbow effect.

Other creatures are also iridescent, creating the shimmering rainbow effect where colors shift as you move. Usually, ... Its skin is almost completely transparent.

You can see right through this little aquarium fish from Thailand: Its skin is almost completely transparent. But when the light hits it just right, its body flickers with shimmering rainbow colors.