Genetic Variations; there is two different color sake. For example there is a green one and also there is red ones.
Overproduction/ Struggle for Survival; Snakes will always produce either enough or more eggs for the environment. They produce up to 100 eggs or even just 3 but not all survive in the environment
Differential Survival and Reproduction; The orange snake is much easier to be located as the green one just blends in and camouflage into the grass so the orange one will be eaten easily by hawks and other predators so the green ones are able to survive and reproduce more than the green ones
Change in gene pool; Since the green ones are not being eaten as much as the orange ones the variation of green ones are going to be able to reproduce. As they reproduce over many years they will become dominant over the orange percentage of population