Principle #1 Variation consist in different colors in fish some maybe a bright color that stand out and others may have the color of a tan.
Principle #2 Overproduction Fishes will always produce more offspring then the environment can handle, not all the offspring will survive.
Principle #3 Differential Survival and Reproduction The blue fish are the ones that will always be easy to spot in a sandy environment. The fish that camouflage with the sandy environment will have a better chance of survival.
Principle #3 Differential Survival and Reproduction Since the sandy fish blend very well with the sandy environment they have a better chance of surviving and producing more offspring.
Principle #4 Changes in Gene Pool - Since the fish with the sandy colored fish have a better fitness than the other fish, the gene that has to do with color will be increased in the gene pool and now more fish will be able to camouflage.