I understand that the red
color originated from the buff coloring.
I just wonder if the red INTENSITY is coming from the blue background.
Is there a definitive answer on that?
I fear you will spend a lot of effort trying to get back to that red intensity that you like. I think it comes from a specific genetic combination of buff and blue, so if you breed too far out on one end (say the buff end), you will lose some of what it is that you are looking for. The same, of course, would be true if you only bred him on the blue end.
You are right that it might muddy the waters to breed him with some blue hens. I guess I was trying too hard to be scientific about this. I would like to know what those offspring would look like and what percentage would possibly carry some red coloration. Maybe none, but what if they were crossed with the buff offspring? Then what? While you are at it, might as well start a hatchery!
Based upon what information was presented about his paternal genetics, I would imagine that the simplest and most controlled way to isolate his coloration would be to cross buff with blue enough times to have more than one result like him and then interbreed those. If he is a rare genetic combination then you would probably need a huge population to find enough similar birds, and even then I don't know if they would breed true 100%.
Of course, maybe you could look into cloning. . . it may end up saving you some money.