At around 1:50 it is there - [ame=http://www.youtube.com/watch?v=OLRubZGWXiY]Aquariums - David Saxby's Reef Aquarium (extended version) - YouTube[/ame]
They are just standard yellow tangs with off-coloring. Ive seen several yellow/white and a few black ones. Everynow and then you see them for sale online, usually for a rediculous price
I think there's an albino version of Yellow tangs and if I'm not mistaken, there's a Black tang species, but that could just be the (rare) colour variants.
They got me at 700 gallon water change!!! At that point I figured this guy is a multimillionaire and has the time to spend 3-4 days a month doing a 20% water change!!
Only price info on the piebald tang I could find said easily 20X's regular yellow tang price and one forum said that one sold for $6000.
Also, you can seach David Saxby and can find newer updates on this tank. Amazing.
Says he completely stripped the original tank in 2009. This is what he did with it.
[ame]http://www.youtube.com/watch?v=PmwBaaMS8M4&feature=mfu_in_order&list=UL[/ame]