There are a number of colors now being bred:
Sable (the most common): Marked and masked like racoons, it's easy to understand their popularity. Sables range widely from light to dark, depending on the shade of both the underfur and guard hairs. The underfur ranges from white to beige. This fur will sometimes have a slight golden cast to it. The guard hairs are longer and are black. A well-marked sable ferret should have a definite mask or hood pattern over the face. The preferred nose color is black to match the "trim". The face should be short and broad.
Red-eyed White: This color is frequently referred to as albino. Red-eyed whites range in color from white to golden; some are albinos and some are not. It is only through breeding that this can be determined. Noses are, of course, pink. It is especially important in the whites for the animal to have a short, broad head. A ferret should in no way resemble a rat.
Silver-mitt: The sterling silver-mitt is white or off-white. The guard hair contains both black and white strands. This mix is what accounts for the silvery appearance. A silver-mitt ferret will also have four white feet and a white bib. The eyes appear black but are frequently a deep burgundy.
Sterling Silver: The sterling silver ferret is marked like the silver-mitt. The difference is in the ratio of black to white guard hairs: the sterling silver has considerably more white strands in the guard hair, thus giving it a much paler appearance than the regular medium silver shade.
White-footed Sable: This ferret is marked like a standard sable ferret but has four white feet and a white throat patch. They do not all show the throat characteristic. The white-footed sables do not have white guard hairs as do the silvers. Noses are generally black.
Butterscotch: The underfur of the butterscotch ferret is the same as that of the sable. However, the guard hairs, leggings, and mask or hood patterns are butterscotch rather than black. Noses are generally butterscotch to match the guards.
White-footed Butterscotch: This color is still relatively rare. Marked like a butterscotch, this ferret has the four white feet and white throat patch of the silver-mitts.
Cinnamon: Truly beautiful, this color is still rare. The underfur is white or off-white. The guard hair is the rich red-brown color of cinnamon.
Black-eyed Whites: This is a color that ferret breeders have been trying to obtain for years. This is still a relatively rare color, but it is now possible to obtain black-eyes whites as pets.
Spotted: A few spotted ferrets are seen each year. Spotting most often appears on the stomach but occasionally also covers the back. The back pattern generally disappears with the adult coat. Spotted kits often have "possum-looking" markings on their faces. We now see spotted adults with white bodies and a striking splash of black at the back of one leg. These are very rare.
Source: Ferrets; A Complete Pet Owner's Manual; E. Lynn("Fox") and Chuck Morton