I tried posting this in the iMac section, but got no response. Basically I've had my iMac 27" for a while, and just ignored this annoying issue where there are coloured marks/dots over photos in Aperture. This was the case with Aperture 2 and continues to be the case with Aperture 3. Sometimes they are green and sometimes they are red. It happens regardless of which lens I am using, and if I import the same photos to any of my other macs they are totally fine. Anyone got any idea what's wrong? Here are two examples ( simple screenshots of what I see in Aperture..if I export the photo it will show up fine): PS. I shoot all my photos in RAW format and use a Nikon D80.