Dark Brahma hens - Why do their colours appear different?

[Papaye]

Hi.

Two weeks ago, I have bought two Dark Brahma hens from a breeder.

...Hens that I was told were born in June...

Here they are :

Given they come from the same place, I find it kind of weird they are so easily distinguishable from one another.
Indeed, as you can see : one hen is on the lighter side, and the other one is clearly darker than her...

Not that it bothers me - in fact, I LIKE being able to tell them apart -, but I would like to know what is happening here...?
I have done some research on the Internet, but I have ultimately failed to find information.

So, here I am to ask about it : is it normal for two Dark Brahma hens to look so different from each other, or could a specific, additional gene be affecting one of the hens' plumage here?

(I know the breeder also sells Golden Partridge Brahma chickens, BUT : I don' know if he owns other colours too, since I only asked him what he still had to sell two weeks ago!)

► In case one of the girls does have an additional gene : what could I then expect from breeding this girl to a Dark Brahma rooster, or even to a Black Copper Marans?

In fact, what can I even expect from breeding a (normal) Dark Brahma hen to a Black Copper Marans rooster?
Not only about colours, but about penciling too...?

...Thank you in advance to the ones who will reply!

 

[ve]

My unprofessional opinion is that the lighter one is missing one copy of the Pattern gene and maybe some melanisers.

 

[Papaye]

My unprofessional opinion is that the lighter one is missing one copy of the Pattern gene and maybe some melanisers.

Thank you for answering!

By "the lighter one is missing one copy of the Pattern gene", you mean she is "Pg/pg+"...?
Which would thus make "Pg" dominant, right?

I am not very familiar with chicken colour genetics, but I would guess it could thus happen if one parent is a Dark Brahma, and the other one a Light Brahma...?

 

[JedJackson]

I'm guessing somewhere in the background of the pale bird a light Brahma was crossed in. It's larger size also could be a sign of that since light Brahmas are typically larger than dark Brahmas.

This variety is usually consistent for color, from what I've seen, so I don't think it is just natural color variation in this case.