Angle and reflection would certainly play a part. But I was told by a body shop (and their DuPont Rep) that it also has to do with the material. Look at almost every car at the bumper (usually poly)/fender (metal) and its slightly off.I agree and seeing the same paint and color on two panel that are not exactly align at the same angle can make them look slightly different. Presumably, the way the light is reflected at a different angle or something reflected off the car from landscape or sky.
My gut reaction to that photo is if it were diamond graphite versus regular old silver.