The term "white tang" is used to describe a melanistic variant of Zebrasoma flavescens (or yellow tang) that is collected in Hawaii... these are uber-rare, and many people dive their lives away in Hawaii and never see one. They've entered the hobby here and there through the years at very high prices... I've compiled a few images of these guys... each is an individual shown a different amount of melanism... They are perfectly healthy otherwise, and retain their color in captivity...
Many aberations are common through the seven species of Zebrasoma... I have this yellow form of Zebrasoma scopas... the most yellow I've seen...
The black tang mentioned above is Zebrasoma rostratum and while it has a range beyond Christmas Island in the Pacific, that is the only place it's regularly collected... I've got two of these guys.. one now about six inches I've had for years that's in the center of this shot... taken with flash under actinics only at feeding time...
I also recently added this little black tang to a smaller system this past weekend... he;s about two inches...
The rarest of the seven Zebrasoma (black tangs are the second rarest) is Zebrasoma gemmatum... the gem tang... this guy is not mine...
Some other Zebrasoma variants are shown below...
A whacky scopas...
A whacky variant that at least has some Z. rostratum in him judging from the nose length...
My favorite example of melanism is shown in my favorite angel... the regal... these guys are collected in the Maldives and usually go to Japan... I've heard of one that came to the states and wholesaled for $1500 in LA... I have a trio of Red Sea regular guys, but it'd be great to add one of these...