What I see on your photo is patch of light on the left of the black device and in the center of the middle one that is making those devices look lighter. The background on the left device could also be not white but one of the gray shades.
If you have the devices make a photo of every device in the same exact spot with M setting on the photo camera or make 3 photos shuffling the devices. And don't show the default off screen because it could be other gray level than white (was on one of the devices I had). Probably the best way to compare would be to show a white space below some text in an ebook.
Sorry for the distrust.
