Octopus

This is amazing!!! Here's some info from Wikipedia on how it happens...

An octopus's camouflage is aided by certain specialized skin cells which can change the apparent color, opacity, and reflectiveness of the epidermis. Chromatophoresiridophores, and leucophores (white).^[16] This color-changing ability can also be used to communicate with or warn other octopuses. The very venomous blue-ringed octopus becomes bright yellow with blue rings when it is provoked. Octopuses can use muscles in the skin to change the texture of their mantle in order to achieve a greater camouflage. In some species the mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises. However in some species skin anatomy is limited to relatively patternless shades of one color, and limited skin texture. It is thought that octopuses that are day-active and/or live in complex habitats such as coral reefs have evolved more complex skin than their nocturnal and/or sand-dwelling relatives. contain yellow, orange, red, brown, or black pigments; most species have three of these colors, while some have two or four. Other color-changing cells are reflective