Question: how can the human eye see so many colours ?

Omar Mahroo answered on 15 Jan 2019:

The cells in our eye that can detect light in daylight levels are called cones. They have pigments in them that sense light. There are three types of cone, each with a different type of pigment. One pigment is more sensitive to red light, another is more sensitive to green light, and another more sensitive to blue light. Colours are made up of different combinations of light, and our eye and brain put the signals from these cones together so we can see colours. Interestingly, other cells in our eye called rods let us see in low light levels. These have only one type of pigment, which is why our vision in low light levels is black and white.