Another scenario is that the Buff Leghorn bred was id+/id+ but id+ pigment diluted by Di/Di Dilute mutation. Di is incompletely dominant, with Di/di+ id+/id+ (male) or id+/- (female) showing intermediate leg pigment. So if you crossed a Di/Di id+/id+ Buff male with Id/- Brown Leghorn female, all F1 sons (Id/id+) would have yellow legs & all F1 daughters (id+/-) would have willow legs.
This is what was found with Brumbaugh & Hollander's tested Buff Minorca rooster, ie Di/Di diluted id+ dermal pigment.
This depends on if you get any yellow-legged F1 daughters (then probably Htul's scenario, ie rooster het for Id/id+).
This must be the case because every male is yellow skinned and every female is willow color. All the buff males are from the same bloodline of show birds so buff minorcas may have been used at one time.
I was only attempting to learn if blue or lavender were involved with the buff color, so I was surprised to get green shanked hens and no blue feathers. It'll take another generation to determine whether lavender is involved or not.
Thank You All for your help.