The Cuckoo Marans barring is very messy in appearance compared to a Barred Rock or other varieties of barred birds....don't know why, just is.
Cuckoo Marans should have light pinkish white legs and the bottoms of the feet should be pink. Toe nails should be white. No yellow legs in Marans. Can't really tell what color this chicks feet and legs are.
Do you have another photo of this chicks comb? & How old is this chick?