When bought I am black, when burnt becomes red, and white when cooled. Who am I?

In a circular room, I'm wall art. In a square room, wall to wall to wall to wall art. Now photos also play a part. 'More' or this mode on your camera might be a good place to start.

I come from high above, dark and with a magnet quality. I am said to have changed the world dramatically.

You may desire loots, but first have a rest on this, and looks backwards.

Instead of holding anything medical, This person holds only a screwdriver, But the screwdriver is not really a screwdriver, He only has a phonebox, Which is the reason why he can travel, Who is that?