Why is her comb so dark?

[Livia Ammon]

I have a pullet who is a ‘Midnight Majesty Marans’, but her comb is way darker than her two ‘sisters’ combs. They have a reddish comb, but she has a pitch black comb still. She is 16 weeks old, and hatched in early February. I included a picture. Any good ideas on what could be going on?

 

[nuthatched]

Skin pigment, she's a melanistic