Just as I suspected the adapter has a small raised edge that can ride on the inner raise of the bearing if it touches at all. Looks good from the pics, and where you have the "O"-ring looks to be where it should be mounted. Kind of a slight buffer for the wheel to snug the fit when it is tightened up. The color only matters when you have the wheels off anyway since the wheels cover the adapter. Get a little mud on it and you won't notice.
