My black english orpington chicks look mottled. Is this possible?

[southerngirl29]

5 of the chicks I hatched from my blue English Orpingtons were black. 3 of them are solid black, 2 of them are black with white flecks all over. It's driving me crazy not being able to figure this out. Is this common? Is mottling like a genetic mutation thing (like frizzles) or is it a different color all together? I'd be thrilled if I ended up with some mottled orps! But I don't really think that's possible. But something is up, because these little chicks are speckled. They are a month old, and have the majority of their feathers.
Does it mean they are roosters maybe? Someone please enlighten me!

 

[1muttsfan]

Chick coloration is sometimes different from adult. The spots may disappear when the get their adult plumage.