I just started with Dorking chickens. My first breeding of some Sandhill birds I received got me blue, may be laced and a reddish many call Clay in the Dorking group. the father was a colored, mothers were either a darkish gray, with reddish breast and black head, or a kind of messed up birchen they said... I was told if I bred them to black, I might be able to get a blue line going. I have put a black Sandhill Dorking rooster with them, (but Sandhill said they had to cross their blacks with reds to prevent inbreeding issues, so some of the blacks I got this year do show some red in some of them...the rooster I put with the blue and clays is not showing red. (I also am rebreeding the orginal rooster to those hens and 2 others to see if it shows up again). I have a book that explains waterflowl colors, but not one for chickens as I was raising waterfowl for over a decade.