I have two hatchery stock LF blue cochin pullets. Right now one is a light gray and one is a dark gray. Can anyone with blue experience tell me if they will remain different shades as they get older? These are nothing fancy, and it doesn't really matter, but I just like a colorful flock.
Yes they will stay different shades. Looks like you have a blue and a blue splash.
Blue is a dilute gene which delutes the color black to blue. It can dilute a little to quite a bit so they can range from light blue to almost black.
If the chick gets one blue gene it is blue if it gets two blue genes it is a splash (blue) with the splash the first gene delutes the black color away then the second gene dilutes most of the blue away also. Search "splash cochins". Most are while or white with a slight blue tint with random blue feathers here and there.
Your two will look very different when grown.
One on the left is Splash. One on the right is Blue. They are two different colors that result from breeding blue to blue. Both blue and splash are genetically black birds with the addition of the blue gene. Add one blue gene to a black bird and you get blue. Add two blue genes and you get splash. Breed two blues together and you have possibility of blue, black or splash chicks. It's the same no matter what breed. I've had BBS (blue, black, splash) Orpingtons, Ameraucanas and Plymouth Rocks.