Algodoo

Cats cannot see lime green over the color of the background. (well, not much) However they can see pink like it was a sore thumb. Hence the color scheme. Using this, you can clone more lime green outline balls to make the pink balls courses more random, And you can add more pink balls to make it more difficult for your cat to distinquish wich is wich. YOu can also play it yourslef and click on the pin kballs to delete them.