The value of colouration in the evolutionary theory depends on the solution of three factors as follows:
1. Vision of Predators
The distinct and marked colouration of the animals which a human eye is able to perceive may not be so the eyes of a predator wjiose vision might be sufficiently different from that of man.
The predators might depend ultraviolet or infra red vision. Intensive investigations have shown that though some animals (which appear protectively coloured to the human eye) are not protectively coloured when photographed by the type of light used by their usual enemies, yet there are many which are so coloured.
ADVERTISEMENTS:
At the same time, it is very likely that many organisms which we do not suspect of being protectively coloured may appear so if photographed at the appropriate wave length.
2. Distastefulness of Models
There are many workers who argue that the distastefulness of many insects has never been proved and that it is not genuine. However, the experiments of Brower prove that some aposematic butterflies are in fact distasteful for Jays which had been conditioned, rejected both models and mimics, while the unconditioned birds took the mimic readily.