I have a Dell 2408WFP monitor and I would like to use it as a second monitor with my macbook pro (Not the unibody one the version before that one) to be able to have a big screen to use photoshop etc.

However when I get it up and running I have an issue with photo shop. I have calibrated the monitors using a spyder 3 elite to get the best out of the macbook and monitor screen. When i open a photo shop file on the mbp screen and drag it across to the dell the colours are all fine even on the dell monitor however when i release the mouse button the window i have dragged to begin work the colours change.

I am using a dvi cable to connect directly to the monitor if that helps with this at all.

Any ideas why this is happening??