Just bought a magazine today with an article on diseases...It says that velvet is similar to ich, except the spots are a lot smaller than ich and, "show up as an almost gold color. It is a bit more difficult to eradicate [than ich]....but velvet does respond well to aquarium medications designed for use against it."
The same article defines symptoms of fungal infections as, "frayed fins and gray, slimy skin. The fish swims erratically and flashes almost constantly, which causes patches of skin to slough off, leaving bare red areas." It also states that "If one fish is affected, it's likely that all fish in the aquarium are infected. Fungus is a fast fish killer. Cottonlike tufts of fungus show up on the outside of the fish -and at the same time, the fungus is growing into the tissues of the fish...fungus can show up when the fish has any wound or disease...net it into a seperate container of clean aquarium water with potassium permanganate for 30 minutes."
There is also a picture of a fish with hole-in-the-head disease where it looks like it has white patches, which I guess are actually where the skin is gone. This is apparently from an intestinal parasite, and is common in discus and oscars.
Hope that helps some.