Koi fish colors?

Question

why are the babies staying black and why are they not changing colors?

Answer 1

do you know the colors of the parent stock?  How many koi did you use to breed?  usual doing here is 3 different male one female.

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Answer 2

wen koi breed only a small percentage will show koi colour. most will look like common carp. this is because (koi) is a mutation of common carp. its all about the genetics.