I'm leaning more towards Exchequer Leghorn, he still hasn't got his adult feathers yet thought. It can be frustrating to wait some times.
I just hatched some black Penedesenca chicks yesterday from a breeder, and one of the chicks looks mottled. Mottling is resessive, so I guess it could be floating around in her flock. She sent me a chart saying what eggs where from different pens, but I didn't number the eggs , so if it does end up being mottled, I wouldn't be able to tell them which pen it came out of. Now to wait 3-4 months.