Has anyone observed this strange behaviour: I have a MBP connected to a 23" ACD. I calibrated both screens. I open a picture in Photoshop and save it including the corresponding color profile to the disk. Then I open it with one of Apples applications, for example Preview, and display the Picture both in Preview and in Photoshop next to each other on the ACD. When both screen are switched on the pictures look the same as it would be expected. The strange thing is when only the ACD is used and the internal display of the MBP is deactivated but all other settings are as they were before. Then the pictures are displayed differently by both applications. I think the one changing is Preview. The color profile for the ACD is the same in both cases. In both cases the main screen is on the ACD. Did anyone experience the same or does anyone know the reason for this? Thanks for your answers.