They have to be Db because Co lightens them to Black Tailed Buff. the Co gene lightens the hens as well as the males. The Db gene does not lighten red pigment too the extent that Co will. There is no Dun in the majority of the birds I have seen. Dun would only lighten the Black areas of e plumage and does not effect red pigment in any way. I have worked with the Dun gene in many different breeds for twenty years and know its effect well. The reason they are so variable may be due to underlying genes. Dark ones may be homozygous for Mh were light ones are heterozygous or not have Mh at all. Cream or white varients may carry a gene like recessive white or Opal. Tim