the eumelanin is responsible for the black, chocolate, and cinnamon colours on cats! it's a common misconception that colours such as grey and white are coat colours (in the same sense that black and brown are), but they are controlled by something completely different.
the other colour a cat's fur can be in red, which is controlled by the pheomelanin.
if you have any knowledge of genetics, you would know that certain alleles are dominate over others. in this case, black in dominant to both chocolate and cinnmon, chocolate is recessive to black but dominant to cinnamon, and cinnamon is recessive to both. However, red is dominant to all of the eumelanin colours!