Come ottenere il bianco columbia

Interesting question you ask here . A similar trying is done in the Moroseta.
When you want only speak about the phenotype than you can only speak of the end of the story but to come to the end of a story you first need to follow a certain road and that road is the "genetic road".
Look for see the good Columbia drawing the phenotype of Black/white Columbia in the Bahma chickens (also here : freeforumzone.leonardo.it/discussione.aspx?idd=9578634)
What is a "Columbia" build of ? Not only of the gene "columbia" !
What is needed :
1. E-locus : eb/eb (is the ground-color for can have the Columbia working out)
2. S-locus : S/S - S/- (is needed to have pure white coloration without restants of gold)
3. Co-locus : Co/Co (is needed to push ALL the black pigment to the endings, neck, tail, wingpens, feetfeathers if present)
What is NOT needed :
1. Ml-locus : ml+/ml+ (if Ml is present you get Quail = dark pigmentation on the back)
2. Pg-locus : pg+/pg+ (if Pg is present you get Laced = dark lacing on the wingbows)
3. Db-locus : db+/db+ (if Db is present you get Blacktail = NO dark pigment in the neck)
So to breed the Columbia drawing you need to SELECT the needed genes and eliminate the not wanted genes.