Though it is a normal phenomenon in several species of Birds, Fish, Reptiles, Amphibians and some Mammals, Tetrachromacy is a prodigy in Humans.
Generally, we have 3 colour channels i. e, L, M, S cones responsible for colour vision. But having an extra channel leads to a perceptual difference altogether. This is a rare feet but the literature suggests that almost 12% of women may have this supervision due to a mutation on the X chromosome. If a trichromat can appreciate 1 million colours than a tetrachromat can appreciate 100 million colours.