As mentioned above, light perception happens in the retina, which is made of thin layers of cells. There are 2 types of light-detecting cells — rods and cones.

Cones are sensitive to different colors, so they help us distinguish red, green, and blue. When looking at one of these, a particular cone is activated. Then they send the information to our brains.
Rods, on the other hand, can help us see different levels of light.

So, for example, when seeing something red, the cone that is in charge of perceiving that color is activated. But if you were looking at something yellow, the red and green cones would activate since yellow is close to these 2 colors.

Since normal color vision uses all 3 types of cones to perceive the light, we call it trichromacy. On the other hand, people who have dichromatic color vision have only 2 types of cones that function correctly. There are 3 types of dichromatic color vision.

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