In a statement to Gizmodo, Apple publicly acknowledged the vexing display issues plaguing its latest iMac models. The symptoms of these issues, which mostly affect the 27-inch model, include yellow discoloration and screen flickering. In its statement Apple said, "We've addressed the issues that caused display flickering and yellow tint. Customers concerned that their iMac is affected should contact AppleCare." While the company has been too slow in addressing this problem, better late than never. follow link
Extract Directly from Time Machine
Normally you use Time Machine to restore lost data in a file like this: within the Time Machine interface, you go back to the time the file was not yet messed up, and you restore it to replace the file you have now.
You can also elect to keep both, but the restored file takes the name and place of the current one. So, if you have made changes since the backup took place that you would like to keep, they are lost, or you have to mess around a bit to merge changes, rename files, and trash the unwanted one.
As an alternative, you can browse the Time Machine backup volume directly in the Finder like any normal disk, navigate through the chronological backup hierarchy, and find the file which contains the lost content.
Once you've found it, you can open it and the current version of the file side-by-side, and copy information from Time Machine's version of the file into the current one, without losing any content you put in it since the backup was made.
- ExtraBITS for 1 March 2010 (28 Feb 10)
Apple Acknowledges iMac Display Issues to Gizmodo