I'm not exactly sure why this is called Silky. If anyone knows, please comment. In fact, there are two species of dogwood that the Plants Database calls Silky, this one and Cornus amomum. Some folks call this one Swamp or Pale Dogwood, while other folks consider them both to be subspecies of the same species. Take your choice.
The easiest way to distinguish this one from Gray and Roughleaf is to wait for the berries, which are purple. Other than that, the flowerheads tend to be more flat and stick out beyond the leaves.