My screen looks like it has an oil slick on it. What's with the rainbow?
This is a phenomenon commonly referred to as "interference patterns" or "Newton's rings". It occurs primarily with non-matte screen protectors that do not adhere directly to the device's screen, and it tends to be most pronounced under bright, direct lighting, particularly fluorescent lighting.
Unfortunately, there is no known solution that will completely eliminate this effect. Fortunately, when the device is turned on and the screen is effectively back-lighting the viewing area, the effect is dramatically reduced.