Kbase Article of the Week: iMac G5 (iSight): Built-in iSight Camera Produces Blue or Green Pictures →

Apple Support:

When you take pictures with the built-in iSight camera in your iMac G5 (iSight), the resulting images may look blue or green in Photo Booth or iChat instead of full color.

This can happen when your display’s Colors setting is set to “Thousands” in the Displays pane of System Preferences. To fix your photos, just modify the settings to display millions of colors instead of thousands.