Cream Legbars are supposed to be pure for the blue egg gene.
So any son or daughter of a Cream Legbar would have to inherit one copy of the blue egg gene from them.
So any daughter of a Cream Legbar should lay eggs that are some shade of blue or green.
If your hen lays a peach colored egg, then she did not inherit the blue egg gene from her father, which means he had at least one copy of the gene for not-blue eggs. So he was missing a gene that a pure Cream Legbar is SUPPOSED to have.
Either that rooster was not really a pure Cream Legbar, or he was "pure" but poor quality (with "quality" meaning "having the genes the breed is supposed to have.")