When I first adopted Riley, I bought her a kitty litter "house". It has a enclosed lid with a flap door. It gives her a bit of privacy (not that she cares, I'm sure) and it keeps potential odours at bay. I chose the litter "house" in red because it's my favourite colour, but I've grown tired of it. As I was in the midst of painting our bathroom, I thought I'd quickly give hers an update as well.
The top is gray, so I just left it as is. I took off the bottom and quickly sanded it before giving it a coat of spray primer. I very lightly sanded the surface after the primer dried, and then sprayed a coat of white glossy paint. I lightly sanded after that coat too, and then sprayed 2 more coats of white. I didn't paint the inside because 1. it's not visible and 2. I don't want to risk Riley ingesting the paint.
Here are the pics: