When you said 3 new hens, I assumed you just got them, not raised them from chicks.
Dark brown egg laying breeds in order of color intensity are Marans, Penedesenca, Empordanesa, Welsummer, Barneveler and Langshan.
Some lines will always be darker than others.
It is a trait that must be...
OK. Try leaving the window wide open.
The building I have with the smallest window has a fan in the window blowing onto the roost year round. The hens earliest to retire, tend to find the best spot in front of the fan regardless of how cold it is.
Figure out a way to lock some in. Perhaps create...
New birds don't know what home is until they've slept in there many nights in a row.
If they are unfamiliar with their surroundings, the bed of a pickup truck, a chainlink fence, a tree branch, the rail of your deck or the roof of your house all seem like a good place to sleep to them.
They have to be locked up in the coop for days before they imprint that it is a safe and comfortable place to sleep and develop the habit of going in at dusk.
How many birds and how much floor space in sq. ft.?
How much ventilation?
As new birds, they don't feel comfortable chumming up and...