I also experienced this issue.
Machine: 2010 13" MacBook Pro 2.4 GHz Intel Core 2 Duo (Model Identifier: MacBookPro7,1), connected to display via mini display port to DVI adapter. All system updates were current (10.6.7, etc.)
General symptom: after being plugged in to an external monitor in extended desktop mode, the machine would eventually get in a state where each of the two screens had a solid color on them. Colors were usually pink and white, but seemed to be dependent on what was on the screen at the time (pink and white are prominent in the standard Mac OS desktop background, which is when I saw those colors). Nothing seemed to resolve the issue other than shutting down and restarting the machine (tried reconnecting the mini display port. What applications were running, etc. seemed to have no bearing (saw the issue once on the login screen and several times in Finder with no other applications running). Symptoms occurred anywhere from 5 minutes to and hour and half after connecting the display. Typically within 20 minutes though.
Some notes:
- We have three identical machines at our office and this issue was only happening on one of them.
- Issue did not reproduce with every monitor in our office (issue did not seem to occur with smaller monitors), but reproduced with most of the larger monitors in our office including 3 identical Samsung SyncMaster B2430 a Samsung SyncMaster B2330 and a Dell widescreen monitor.
Our machine is covered under AppleCare so I contacted Apple by phone and made arrangements to mail the machine in for service. Unfortunately, the repair facility could not reproduce the issue, so they returned it back to us without doing any work assuring me that the machine was up to specification.
The issue still occurred after I received it back, so I took the machine into an Apple Store and they checked it in for repair. Though the Genius suggested they would likely replace the logic board, I got a call next day saying they weren't able to reproduce. The representative that I spoke to initially suggested that the problem was with our display, but once I explained we had no less than five different displays that produced the problem as well as a few that did not, he asked me to bring my monitor into the store.
So I carted a monitor that had been connected to the macine into the Apple Store. The issue did not reproduce in the 10 minutes that I was with the Genius, but based on the troubleshooting I had already done and described to him, he felt it was safe to conclude the machine needed the logic board replaced (which has the GPU integrated) so he put in an order to have that done. He apologized for me having to bring my monitor into the store.
I received the machine back on Monday night. It has now been running for over 24 hours straight without any issue.
So, my advice to anyone who is having this issue, be persistent in seeking support, the issue can be difficult to reproduce since it does not happen with all displays. You may want to start by pointing Apple to this thread and politely suggesting you may need a new logic board if you have a similar machine with the same exact symptoms.