Emerald Cory - Color Change?

[ricester61]

About two weeks ago, I replaced our original neon, multi-colored gravel with some black sand. Cory's seem to be much happier - they dig trenches in it and seem a bit friskier.

We have noticed, though, that our two emerald green cory's are a heckuva lot darker now. They almost seem as black as the sand. Can these guys change color to match their surroundings? Or, is this just an optical illusion caused by the darker background?

 

[Leopardess]

It's a bit of both. The lighter color probably reflected off the body a bit, whereas the darker color does not. Also, fish feel safer with dark substrates because they instinctually "know" that they are harder to see from above, among other reasons. So, fish will often darken when they are near dark substrates, partly because they feel less stressed.