So, the retina is basically this portion in the back of the eye, and the retina contains specialized types of cells known as the rods and cones. Now, rods and cones contain special photochemicals that are capable of detecting our life, absorbing the photons of light. And this photochemical is known as a pigment. Now, the rods contain a pigment known as rhodopsin. Now, the thing about radopsin is it can actually absorb all the wavelengths of visible light. And that means our rods cannot actually distinguish the different colors.