There are two different populations of bunnies. There is a population of bunnies with white fur and a population of bunnies with brown fur.
Change in Gene Pool
When bunnies have offspring they have multiple babies per litter (1 to 14 bunnies). A lot of these bunnies are eaten by predators.
The bunnies with the brown fur are surviving and reproducing because they are camouflaging which allows them to hide from their predators. The bunnies with the white fur are seen more by the predators so they aren't surviving as much as the other group of bunnies.
Over time the gene pool will have more bunnies with brown fur because the reproduced, passing on the genes for brown fur.