dyed fish are not something interesting and cool, i'll tell you that. there are two methods of dying a fish.
in the first method, the fish is dipped in a chemical that removes his protective slime coat (the thing that protects them from diseases) and then dipped into a colored dye which leeches into the skin. finally he is redipped in a poor copy of a slime coat, and the result is a fish that is 'colored'.
second method is probably more painful. the fish is literally injected with the dye. a needle is forced into the spine, and the colored dye is injected. the only produces a fish with the top half or a crescent shape on the back that is colored.
dyes leech out and get eaten away after a while, making the whole unbearable process worthless as the colored fish soon becomes a regular albino or glass fish.