My substrate is a mix of red, white and blue. My gf's little brother used to have the tank and his parents wanted a patriotic gravel, I guess. Its not very dull so I wasn't sure if the fish would change with their environment. The female guppies are the only ones that have changed color at all. The male guppy went dull for a little while after I got them and now is back to his bright colorful self.pondfreak4365 said:Hi Guppymonkey,
I had a similar question recently about color changes in female guppies. The information I found stated that the females will change color to match the substrate. Mine are in a black lined patio pond...the females turned black too, but still have yellow spotting on their tails. Is your substrate a light color?