Trout are not the only fish that can change color. Flounders, like the one on the right, are masters of this skill.
How do they do it? They use special cells called chromatophores! For a quick intro to fish coloration. You can see chromatophores up-close here. Fascinating stuff!
Fish living in darker locations tend to take on darker colors, but did you know that blind fish turn dark colors, as well? Check out the links in "On-line Resources" if want to know more.