From both parents.
If you want the darker green color, your best bet would be roosters from a darker egg breed/line as it is basically a darker egg plus the blue eggshell genes. Welsumer or marans would be great choices. Lighter green is from lighter tinted eggs plus the blue eggshell gene. So your cochin(light tan eggs) would likely throw green eggs more towards lighter green shades but you might still be surprised with one or a few on the darker side.
If she is pure for the blue eggshell gene, then all of her daughters will lay eggs in green shades.
If she is not pure for the gene then only half of her daughters will lay green shades with the rest laying tan shades most likely.
If she has a pea comb, keep the daughters that have pea combs, especially if half come out with single combs.
If she has a single comb, there is no way to tell which daughters might be colored egg layers.
