Black Beauty is a variation of Classic Gray that can come up from time to time in Leucistic breeding. They are a variation of Classic Gray that has much bolder and darker black markings, with the dark bands on the fingers as well as a pronounced chin strap which a dark band under the neck. There is also a more pure line out there that is producing darker and darker Black Beauties from a sugar glider named Elvis. The little one in the photo is a super dark Black Face, Black Beauty Male from Melanistic Lines.
The boy pictured here is s actually a Black Face, Black Beauty.