Iridophores are plates of chitin or protein, which can reflect light. They are responsible for the metallic blues, greens, golds, and silvers often seen on cuttlefish. All of these cells can be used in combinations. As well as being able to influence the colour of the light that reflects off their skin, cuttlefish can also affect the light's polarization, which can be used to signal to other animals which sense polarization.