Black porcelain costs about x4 more than standard clay. The minerals and stains used to create the rich, dark colors are expensive and fickle. For that reason, colored porcelain pots tend to cost more than standard pots, and also explains why many of these pots are "Seconds."
Black porcelain isn't truly black, when fired. It's a very dark rich brown.
Another note about porcelain: porcelain is stronger than stoneware (which is already very strong) and more difficult to work with, but is considered the premium of all clay bodies. Therefore, anything porcelain tends to cost more, especially when hand-created.