One of my favorite new features in the most recent Aperture rev is the Brush Tool. Brushes in Aperture offer sophisticated brush edge detection which constantly resamples as the brush moves… meaning that it treats each new area as it’s only edge sample. This is very useful for drawing inside or outside a complex pattern. You can see as the brush moved across the bear it treated each new area as a new edge and painted over both the water and the bear alike, even though Edge Detection is turned on. If you want Aperture to treat this so that the bear isn’t colored over but the water is, you can use a cleaner area to work with. When you hold down the Shift key, it holds the sample from the first click. In the second bear picture that’s what I did and notice that none of the brush changes impacted the bear. It was protected from the changes by the Shift trick.
Give it a try. Use the Shift key in Aperture to protect an area from being impacted by a brush. The Shift key works with a variety of commands in Aperture so a little experimentation can go a long way to filling your Aperture trick bag.