There are four types of butterflies, each of them has a mutation on their DNA sequence that by consequence creates a different amino acid to each butterfly creating four different colored butterflies.
Every day without missing, a green bird comes in search of food (the butterflies), searching in the nearest bushes since the butterflies usually hide in them, as you can see the difference of their traits affect the way they are noticeable making three of them stand out more than the other one, in this case the genetic variation is not favorable to the butterflies with different Genotypes.
With the time butterflies started to adapt themselves into their habitat, changing their appearance in order to hide from the predator that used to came searching for food, leaving only a small percentage of colored butterflies survived.
During the spring season the bushes in which the butterflies used to hide in started to grow some flowers out, making it not possible for them to hide while the phenotype of some butterflies started to change again.
Finding butterflies was getting easier to the predator since the green butterflies were easier to find between the red roses, but it stopped once the butterflies started to reproduce passing down their appearance to their offspring, changing once again the population of butterflies.
At the very end butterflies changed due to natural selection, only a small percentage of green butterflies made it to live in order to reproduce when the flowers die and keep the process going until they get to evolution having an appearance that'll make them survive over many seasons even though some butterflies will die in the process since they are preys and are killed by the predators to keep themselves alive.