Lavender orpington question!

[Strowbridge]

I have 3 lavender orpingtons. 2 hens one roo. I'll attach a picture
They have been seperated from my other coop so I could get hatching eggs. A friend of mine has some hatching right now from them and some are coming out black. Ive heard of the black split lavender but can someone explain how this would work and why I might be getting black chicks from all lavender parents?

 

[jwcarlson]

How long have they been separated?

 

[debid]

Either not separated long enough, eggs mixed up after collecting, or you have mistaken a light blue bird for lavender.

 

[Strowbridge]

How long have they been separated?

35 days, so only like a week before these eggs went in. Some have hatched out lavender and some are black