LF white and dark cornish

[Konradrueb]

Feather sexing.

 

[Ridgerunner]

You can read what Tadkerson (a genetics expert) had to say about feather sexing in the first post in this thread. You will see that he lists "cornish" in the slow feathering group. It doesn't matter if it is light or dark cornish.

https://www.backyardchickens.com/threads/sex-linked-information.261208/

For feather sexing to work the mother has to have the dominant slow-feathering gene and the father has to be pure for the recessive fast-feathering gene. For our purposes that generally means crossing two different breeds. And you have to know for sure that those flocks are pure for the genes they are supposed to have.