There is a bug with the Mac App Store version of the app that affects certain Macs that are a few years old.  The stage doesn't appear, or appears a pale blue, and the Scratch Cat sprite doesn't appear. We're working on a fix for this.

The good news is that this only affects the Mac App Store version. If you're running into those problems, we recommend getting the "direct download" version from This version does not show that behavior.