IMO it doesn't always matter.
Quoted directly from Bill Van Patten of FabulousFinch.com: "in addition to the negatives of breeding cross head morphs, there is also a positive that is yet unexplained. Mike [Fidler] has seen that when Red Heads are paired to only Red Heads, the head color goes "off" over 5 or 6 generations. So he breeds back to a Black head every 4th generation or so to maintain the brilliant red in his lines."
Here is a perfect example:
RH/OH Purple/White Blue Cock x RH Purple/White Normal Hen
Hen Offspring #1 (Click on thumbnail for larger image):
th_IMG_1070.jpg
Hen Offspring #2 (Click on thumbnail for larger image):
th_IMG_1114.jpg
So - even when pairing two RH together I still got one random muddy RH hen, despite her sibling being almost as bright as a cock.
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