The size of the chicks comb and wattle are a good indication that it's a cockerel.
Also, female Lemon Cuckoo Orps are only single factor barred, resulting in a darker overall buff color with a fainter barring. This bird looks to be double factor barred, something that only male birds can be.
What you might be seeing in her tail/wing is Khaki, sometimes Buff birds carry the Dun gene. You typically need two copies of the Dun gene to express Khaki (1 copy of Dun from each parent bird) so I'm not positive if that's exactly what it is.
Very pretty girls, it looks like you're project...
Sumatras do not have black skin, nor do they have black bones. The only thing they share in common with Silkies is that they both do have dark faces.
I raise LF Sumatras in Black, Blue, Dun and Platinum.
Like I mentioned in my previous post yellow skin is a recessive trait that can "hide"...
I wouldn't suggest using Blue Sumatras or Blue Andalusians to try to get better lacing in your Blue Ameraucanas. Both breeds have yellow skin. This is not something that you want to breed into your Ameraucana liine, yellow skin is a trait that can "hide" recessively in birds and generations...
If they are something you really want, then what does the price matter?
I would however want to see LOTS of pictures of the parent birds, to evaluate type, feather quality, etc. I wouldn't want to pay $170 for a bird no better than hatchery quality. If you're okay with run of the mill birds...