Bingowings, the inescapable problem in that shot is that the R2 unit, whatever colour it's painted, just looks like R2 D2. It's riding alongside C-3PO and there are only four characters being focused on in the frame, Ben and Luke at the front and the two droids behind.

I just don't see how it is ever going to work while R2 is still in the fram there. It was shot that way for a reason, so to expect the shot to look like it's focusing on Ben, Luke, C-3PO and "some other R2 unit" is a bit unrealistic. I understand where Adywan's coming from, stickler for continuity that he is, but that shot doesn't work.