They are somewhat popular down here in my neck of the woods, SE NC. They don't seem to fair too poorly in the heat, but management of any rabbits in heat is important. I BELIEVE they come in only black, blue and chocolate, but could be wrong. Have you tired the American Rabbit Breeders Association site? They have accepted colors, recognized breed clubs and tons of other info!
The only thing I can think of off hand about the heat is slightly larger ears in buns produced during the summer.....since they cool their systems by circulating more blood thru the ears....and seasonal infertility is common in most breeds due to heat in the summer.
Good Luck!
Anna