He looks like his hackle and other feathers are coming in silver, not gold or red like Welsummers. So I would guess he's silver pencilled Plymouth rock.
He looks silvery to me, but who knows? If he's light gold then maybe he is just a little off in color for a Welsummer. But my hunch is that he's something else, probably a silver pencilled rock. It will be interesting to see what he looks like when older.He looked like a welsummer as a baby but very very light in color; this is him as a baby and now almost one month