The following tip comes from the Apple Pro Training Series: Aperture 2 book published by Peachpit Press.
Let’s look at two adjustment controls in the RAW Fine Tuning controls group: Boost and Hue Boost. Aperture includes a set ofcamera profiles for all supported cameras.These profiles give Aperture specific details about each camera’s imaging characteristics,and are used to determine what color and contrast adjustments should be automatically applied to the RAW file.These adjustments are done to apply the optimal decode based on the manufacturer ofthe camera.
The Boost slider lets you control the degree to which this default adjustment is applied to your image.By default,the Boost slider is set at full strength,so your image appears with the full level ofcorrection.As you drag the slider to the left,the correction is reduced.The Boost slider is handy for times when you feel your images have too much contrast or are a little too saturated.