The Black Russians known today were discovered in Belgium in 1997. The Black is black on the back, sides and belly and the black colouring extends all the way to the roots of the hairs. The Black has white on either side of the nose, paws and white under the chin and often there is white under the chin and sometimes patches of white on the belly.
Some Blacks lighter with age and it is then possible to distinguish a very slightly darker dorsal stripe.

Many Blacks develop silvering (a sprinkling of white hairs particularly around the neck) as they get older and the black colouring lightens. It is thought this is due to a separate "silvering" gene which is heavily linked to the Black gene.

Source: http://www.petwebsite.com/hamsters/black_campbells_russian_hamster.htm