According to my readings/findings different lens "receive" light differently due to the quality of the glass. The "richer" you are referring to (I assume as I don't think you are referring to the CA and sharpness and things like this if color is concerned) is the COLOR that the glass interpret the light coming in. I belive it's the elements that makes up the glass that changes the color incoming which makes the color "pop" or become warmer/cooler.