That's not how it works. It works like this: Imagine all moths are red, but they live on trees with bark that is white. Birds will easily see the moths and eat them. Then, a moth is born that is a slightly lighter shade of red. It has a slightly higher chance of surviving as it matches the bark's colouration slightly more. This continues for 1,000,000 years and one day all the moths will be white and they will all match the color of the trees on which they live.