Of course there are black diamonds. These are not even colored diamonds but occur naturally in black. It is rarer than the colorless diamonds. In fact all the fancy diamonds are rarer than the colorless ones and so more expensive as well. Diamonds occur in a lot of other colors like blue, red, green etc. There is a diamond which changes its color when kept in the dark for more than 24 hours and returns back to its original color as soon as it is exposed to light.