some sea turtles have light colored shells(Atlantic green) and some turtles have dark colored(pacific green)shells.In this senerio the dad has a light colored shell and the mom has a dark colored shell, therefor its off springs will come out with light or darked colored shell.
when the mom lays eggs she lays 100+. She lays them on the beach shore and goes back to the sea wich means the babies are on there own when they are born.When they are born some dont make it to sea some die because they are seen by predators.They are seen because of the color of their shell
the turtles that can be seen in the sand are the dark turtles(pacific green) there for they get eaten and it decrees the population in the environment of darken colored sea turtles. But the light colored turtles (atlantic green) are able to blend in with the sand and make it to sea and increses the population of lighter colored sea turtles
so there for turtles with lighter colored shells have a higher chance of having lighter colored off springs. And if a darkend sea turtles will to mate with a darkend female sea turtle they will have darken colored shell and not many will make it back to the sea.