What breed are these?

[BarredRockin20]

I bought 6 sappire gems and four look the way they’re supposed to and two look completely different. All were black and just started getting this white on their necks. Included are pics of them and also pics of the regular looking sappires beside. Could these two be roosters? I got all 6 as pullets.

 

[InterestingChickens]

All look to be pullets; it is likely just variation within the cross. However, they could be another strain as I'm not familiar with U.S crosses.