Or a legbar rooster over dark egg laying welsummer.You know how cool are Autosexing blue egg layers like the Cream Legbar ares? Well I think it would be even cooler if one would start a "Autosexing Olive Egger" breed..
And it would not be hard at all, just get yourself a few Black Copper Marans, a Cream Legbar rooster and breed back to BCM to get back body and type while keeping sex linked barring, then it would be a matter of making homozygous barred cockerels...
The other way would be to breed Golden Cuckoo Marans breed to Legbar or Ameraucana..
F1 pullets would be autosexing. Cockerels would need the second barring gene so breed pullet back to CCL.
Then its just a matter of keeping the egg color which is standard issue with OEs.