In an experiment, 1000 rodents were released into a light brown sandy area where no rodents previously existed. The rodents' fur color was either brown, black, or tan. There was a known predator of the rodents in the same area. After several generations, what fur color frequency would a researcher expect to see?

It is expected that rodents with brown color have more chances to increase their frequency in the population

Explanation:

The cryptic coloration (or camouflage), is an adaptation that organisms have developed to disguise their appearance, thereby blending in with the surrounding environment. The cryptic coloration is used by organisms as a strategy to hide their identity, movement, and location from their predators. In this case, it is expected that organisms with the same color of the surrounding environment would be the best to be selected by natural selection, i.e., these organisms would have more chances to survive and to reproduce.

that is wrong, its not thymus.