Why Do My Photos Look Different in Aperture Than They Did on the Camera LCD?
Why do my RAW files look different than the JPEGs?
Why do my photos look darker or lighter in the thumbnail and the viewer?
Why do my photos look like they did in the camera for just a few seconds, then change before my eyes in Aperture?
This question was answered at length in this post; Why Do My Photos Look Different in Aperture Than They Did on the Camera LCD?