Yes you want to incubate the darkest eggs your flock produces, But make sure the rooster or roosters you are using have come from the darkest egg possible. Your rooster carries your egg gene.
Take what every roos you have with too much copper on the chest and find someone with hens that have less copper the neck. Use that rooster for those hens.
What do you guys think of this new roo i got from a man that has roo and hens with Cottage Hill bans on their leggs. He does have feathered leggs you cant see in pic.
Thanks