What breed of duck could it be...

Hey all,
I have 4, 2 1/2 week old ducklings. One is a Pekin, one a Rouen, one a Ancona. The last one is a mystery. If only I had a picture to post, but i'm the last person to own a digital camera in the free world!
This duckling is a beautiful steel grey, almost blue color with a yellow chest and belly. Very dark bill and legs. Lighter coloring around it's eyes and bill. At first I thought maybe it was a blue swedish but the hatcherey it came from doesn't sell any swedish ducklings. They do however sell Welsh Harlequin. You think it might be a Welsh? After I had them a week I read where you can sex the Welsh by the bill color. I'm thinking mine might be a male, but it's quack is very loud and sharp. Actually the Pekin is the only one who has a soft quiet quack.
Any thoughts?
Thanks!