There are many brown tabbies out there. But aside from specific breeds like Burmese and Havna Browns, you don’t see a lot of solid brown cats. I personally have only ever seen one (she’s a real cutie). For that matter, I can’t think of any cats that have solid brown patches, the way that other cats haveorange or grey or black patches. Is the brown gene just not that common, or is there some intrinsic trait that makes brown unlikely?
It’s recessive, in a three-level dominance scheme. B is the dominant form = black cat. In fact if you look closely at a black cat in bright sunlight you’ll see that are actually just very, very dark brown. Two further gene variants - one produces brown ( chocolate ), which is recessive to black, but dominant to the final version that produces lighter brown ( cinnamon ).
Further the dominant form of the orange gene also overrides the black gene above.
In addition the piebald gene ( white spotting ) will overlay any of the above ( to the point of occasionally an all white cat with a few non-white hairs - the “giant white spot” phenomenom ).
There’s more, but basically the answer is just that is a more rarely expressed recessive condition relative to other colors.