I know this is an old thread but someone may be looking for the answer. to expand on what FloorCandy posted above. Sex Linked colours are used so you can tell the sex of the chick at hatch by the colour of the Down. Hens have ZW chromosomes and cocks have ZZ. Sex linked genes are on the Z chromosome. Cocks need 2 copies to show the colour and can carry it, hen only need 1 copy to show the colour and can not carry it as they only have one Z chromosome. So if you breed a cock with 2 copies of the gene to a hen with no copies of the genn then all chicks will have 1 copy of the gene and hens will show the colour and cocks will be carriers and not show the colour. If you want to have your own sex linked line, put a carrier cock to a visual he and keep a cock that is visual for the colour and then breed him to non coloured hens.