well it's evolution
when a child is born of 2 animals it gets the combined traits of both parents
some frogs might be green, while others are yellow, due to breeding. unfortunately for the yellow frogs, they live in a lush green forest, with few yellow areas to camouflage in. so all the yellow frogs are eaten by pretadors. sometimes new traits are made with mutations. so it's survival of the fittest and breeding that weeds out the weaker traits. so slowly, the population of frogs changes to not include yellow frogs.
it's natural selection