When I was considering a brown seat for my black bike, I Googled it for images. Here's the link. I didn't get one, but I still think they look good on a black bike.
While I was looking for a new 2-up seat for my Black FXDC over the past couple of weeks I noticed either Mustang or Saddleman (forget which) now has a solo seat with a brown insert. Probably order one sometime in the next few weeks.
i think a brown seat on a black bike looks pretty good. if your not looking for something too drastic you could try a brown insert. below is a pic on red, but it gives you an idea. for me, i didn't want the brown to clash with any of the black trim like the speaker covers.