"..an MIT/Harvard study suggests that a specific type of limpet's shell may hold the key to transparent displays that require no internal light source. The mollusk in question is the blue-rayed limpet which, as its name implies, has bright blue stripes on its translucent shell. It is believed that these are used to make potential predators mistake it for a poisonous snail, which also has blue markings. The iridescent lines appear blue due to the fact that the shell material in those areas reflects the blue spectrum of incoming light, while absorbing other colors so that they don't drown out the blue."
Via Miguel Prazeres