I was hoping to post these photos earlier, but I had trouble tracking them down. This was just a little something, non scientific, that I did a while back.
People usually have a tough time understanding what really happens inside of a safe during a fire. What I did was place a few common items on a cookie sheet, and placed then in an oven at 350 degrees for a half hour.
Here are the items before:
Here are the items after:
You will notice that most of the items weren't really destroyed. The CDs were warped and would no longer play. The photos had turned very dark, with the Polaroid actually being destroyed. The paper did OK, but you may notice in the after photos that it started to darken.
If you compare these photos to others where "shadows" are claimed to be causing the color distortion, you can draw your own conclusions.
I'm not posting these photos to say that this type of damage is bad. It should be expected, as this is what most fire rated safes are designed to do. The thought behind a fire rated safe is to keep paper documents in readable condition. Some damage is to be expected.