Well, what's not to say all the colors leak light the same way? That doesn't definitively prove that its the silver one in that one shot.
When it comes to big budgeted movies, the production design/art department and the continuity people are stickler for details. If they had a silver one used in that scene when the other shots are with the dark grey one, the director would be asking why the hell isn't the phone in the other two shots silver in comparison to the first shot, or why the phone in the first shot isn't dark grey with the other two shots after that (and after that, would potentially lead that person to not work in the industry again after that). In fact, the director would have pointed out the problem of continuity of color between phones during the prop showoff that is normally done in pre-pro.
Trust me, having to work in the art department for a couple of short films, continuity is one of the things that is driven in like a sledge hammer. And if they did receive one silver one with about three dark grey ones, you can guarantee that they either A. wouldn't use it or B. paint it a dark gray to match the others.
But, like you said, unless someone has a picture of the actual prop from an actual presentation in normal lighting, it's safe to say all phones used are dark grey.