I have only read a few of the posts on this leg color issue but here is what I have seen over the years. Yellow legs are usually more pronounced in males in most of the American breeds. Some females ...like Barred rocks have an off color leg color that can be anywhere from greenish yellow to very good yellow. Males very seldom have problems with leg color, but females many times do. Everyone seems to agree that laying will beach out the leg color of females. Personally I have never had sun bleach out the yellow color in legs. I am not saying it can happen, but I haven't seen it happen here. I have seen differences in leg color while judging over the years that seems to be only environmental. There is some evidence that the substrate chickens walk on can change shades of leg color. Shades of color, but not the basic leg color. While laying leg color in females can bleach out to what almost appears to be white.
Feed can intensify color, but not significantly change color. In other words, feed will never make white legs yellow. It will make pale yellow legs bright yellow though. There are several yellow legged American breeds/varieties where yellow legs in females can be a problem. (black rocks...females have dusky legs, partridge rocks, barred rocks, partridge Wynadottes females have off color legs etc etc). The females seem to have the problem with leg color not the males. If I had males with problems with leg color I would look more at my breeding program to fix it than any other reason/cause. IMO if female Dels have leg color problems it is probably coming from the BR influence somewhere back in the original breeding.
The SOP is describing the perfect bird and so far I have never seen a bird that I could not fault in some way.
Walt