Lots and lots of options for the orange-feline aficionado. You can go with Morris; Garfield, if your ginger is portly and likes lasagna; or Tonto, from the fine film Harry and Tonto, although most people haven't heard of that movie, and the ones that have probably cried at the end of it. (It's good, though. Art Carney won an Oscar for it.)
I live with an orange-and-white cat myself. His costume last year? "Melted creamsicle." His costume this year? ..."Melted creamsicle." (He's seventeen and thinks he's a Russian poet. You want to put a hat on that guy, you go ahead. I'll be over here with the Bactine.)
And if your cat is a very bright orange, you can try "traffic cone."
What "costumes" have you given YOUR orange cats? Dazzle us in the comments!