Don't forget the purple balloons...

... and if you are going to send invitations, it should be easy enough to make them fit the cat theme and/or the purple theme. If you can find a cat-shaped cookie cutter and some sturdy purple paper, you're in business. You can also make a streamer-type decoration with those two items, if you accordion-fold the paper and remember to leave a bit of the sides attached, like the paper dolls-holding-hands you made when you were a little girl. And, of course, you can make cat-shaped cookies! You can also do autumn leaves that way, in keeping with Gina's brilliant suggestions. Purple should work well with the golds and yellows of autumn, even the pumpkin-oranges. In fact, if the cat cookie-cutter or stencil you find is smallish, you can paste the purple cat onto a larger, gold-colored leaf shape! Okay, maybe that's going overboard, but you get the idea.