Smear 'Em Up: Battlepaint

If there's one arena-shooter you should play this morning, I'd say it should be Battlepaint. It's not an original concept - you shoot bads and they pop into paint splatters - but the implementation is great fun, and I love the various additional effects, such as your shooter-craft smearing the paint as you whizz about in the arena. It supports one or two players, and it's worth a look.