Why were straight comb blue egg layers important as a parent line? Rose comb is from an inversion on chromosome 7 combined with straight comb on chromosome 1. Most easter eggers, araucanas, and ameraucanas have pea comb which is tightly linked with the blue egg gene on chromosome 1. If I started with pea comb birds, I would have wound up with walnut comb instead of rose comb. The segregation rate for straight comb is 1 in 34 chicks so I would have had to hatch a few thousand to get 20 or 30 that had straight comb. That would cost way too much in feed and time. Which made the straight comb blue egg laying brown leghorns such an easy decision. It saved me YEARS of breeding effort. The brown leghorns also carried the traits for extended laying (up to 300 eggs per year) and lay very large eggs. Them there was the intense blue eggs with no trace of porphyrin (brown egg coating). The positives made them a much better choice than other possibilities such as Cream Crested Legbars. I eliminated legbars based on 5 different genetic negatives, they have a diverse range of colors including barring which would be difficult to eliminate, they lay small to medium size eggs often with green color tones, they have the "crest" of feathers, they lay fewer eggs compared to the brown leghorns, and the coup de grace' was finding evidence that CCL's carry genetics that can significantly reduce both the size and number of eggs produced.
Why not easter eggers? Pea comb, muffs/beards, very diverse feather colors,
Why not Araucanas? One word, rumpless. It is a pita to get rid of once in a flock.
Why not Ameraucanas? Pea comb, muffs/beards, and the E locus would be in conflict with the Silver Lace Wyandottes for many Ameraucana breeds.
I've had a lot of difficulty in maintaining blue eggs while re-focusing the genetics toward laced phenotype. Look closely at the soft poofy tailfeathers of wyandottes and compare them with the fan tail on leghorns. Now if you can stretch your mind a bit, picture a fully laced hen that looks like a wyandotte but has a fan tail which she spreads wide most of the time similar to the way a turkey tom fans his tail to impress the females.
There was a phase where egg colors segregated heavily. I had blue eggs from one parent and brown eggs from the other. When you look at the genes involved, you will see that there is a possibility of a hen that does not have blue eggs and does not have the genes for brown eggs, in other words white eggs. Well, guess what, between 2015 and 2018 I had several hens that laid white eggs. I have not seen a white egg layer since 2018. Note from the post at the top that I have Zinc White from the brown leghorns. This gene reduces porphyrin production dramatically. About half of the current laying hens produce blue eggs with a slight sandy tan tint. So long as zinc white is present, my chickens can't lay a green egg. At most, it will appear tan.
Edit: change blue to green because zinc white restricts chickens from producing green eggs.