Ans. Cones also contain a pigment, known as iodopsin There are three main .types of cones and each type has a specific iodopsin. Each type of cone recognizes one of the three primary colours i.e blue, green and red. If any type of cones is not working well, it becomes difficult to recognize that colour. Such person is also not able to distinguish different colours. This disease is called colour blindness and it is a genetic problem.