Part of the transmitted light is reflected off the back

A portion of the transmitted light then reflects off the back surface.The two reflected waves interact.Usually they cancel each other out,
but when the wavelength of the reflected light matches the distance between the two reflections,they reinforce each other.Green light has a wavelength of about 500 nanometers,so melanosomes that are about 500 nanometers across give off green light,thinner melanosomes give off purple light, and thicker ones give off red light.