Very solid game - simple to execute, but it fits the theme really well. The difficulty also ramps nicely as each level uses the tools in a bit more creative way. There's also a lot of ways this could be easily expanded with different stencils for even more variety.
I think my biggest gripe with the game however is that it's difficult to tell the black color and stencils apart. After applying black coat, it's easier to check what isn't on the mask, rather than what is. Some unique pattern or an outline for the stencils could have easily fixed this.