"There is evidence that environmental color can influence metabolism and weight in rodents. A high school science project found that when mouse cages were surrounded with yellow paper, the mice ate more but lost weight, while when surrounded with blue paper they ate less but gained weight. "
I found this a couple months back and found it quite interesting. Of course I've been trying to find yellow toys and hammocks ever since.
Because my cage is all blue. But all I seem to find are blues and purple at the pet stores