It is estimated that each of the three cone types in the human retina can pick up about 100 different gradations, and that the brain can combine those variations such that the average human can distinguish about one million different colors.
That each of the three cone types in the human retina can pick up about 100 different gradations, and that the brain can combine those variations such that the average human can distinguish about one million different colors. This was what it is estimated.