Oil droplet
Oil droplets are found in the
coloured, while others appear colourless. They are located in the cone inner segment, where they intercept and filter light before it can pass through to the cone outer segment where the opsins are,[3]
the molecules that sense light.
The adaptive advantage of oil droplets is not firmly established. Coloured oil droplets have a cost in that they reduce the amount of light available to the visual system.[4] They also reduce the overlap in spectral sensitivity between different types of cone (e.g. short wavelength sensitive, medium wavelength sensitive etc.). This can be a benefit because it increases the number of colours that can be discriminated, and calculations by Vorobyev (2003) support the hypothesis that this is of net benefit.[3]