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It is a little hard to tell from the photos, but to me it looks like her comb. Silkies have a bumpy comb that sits right above the beak. Because of the fibromelanosis genes that they have, often the comb is black rather than red. If you’re seeing orange/yellow then it’s possible that the comb will end up more on the red side and it is changing colors as the hen matures. Are you sure it is a girl, not a boy? (I only ask as you didn’t mention the age - if it is very young and starting to turn orange then I would guess it is a boy, but if older, like 4 months + then it would indicate girl) Anyways, I would not worry about it, as to me it looks like a normally developing walnut comb.