The first Silver cockerel I had from Kari has yellow legs (although when we were shooting for "willow", one of the judges actually said his legs were technically "willow", yellow with a cast of black pigment), and I've been trying to hold back my darkest eyed/legged chicks, however, he had some good qualities I wished to bring forward. If I have two birds of equal quality and one has lighter legs, I'd dump them. However, if I have light legs with very little other fault and the others I have have autosomal red, squirrel tail, are puny, etc., I'd keep yellow and move forward. You can eliminate it pretty easily through culling in future generations if need be.
As for the colors, check the IBCC website's photo gallery. I've changed out the names and have examples of all 4 of the color varieties we are dealing with so far: (with opinions below being mine, not representing everyone's opinion)
Silver - what we called silver penciled - the birds are not a true penciled and the name would lead to some issues in the future, so we elected to simply call them Silvers. The hens are the lighter variety and imho the prettiest and closest to what seemed to be the ideal coloration for IB hens. The males have white wing tips, the breast at this point appears to come in two variations, either mottled to varying degrees or with patches of white on the breast.
Charcoal - these are the brown chicks without the mottling/striping. They resemble birchens as chicks except they are frosted with brown tips to the chick down, appearing a warm brown. Typically solid in coloration. Adults resemble the Silvers except a darker shade. They look somewhat intermediate between Silver and Birchen and are on the ER base. The cocks appear to be closer to the original Iowa Blue, with dark wing tips (though with varying degree of lacing/stippling) instead of white wing tips. I think they'll also have better lacing on the chest (vs. the more mottled pattern of silver cock birds).
Smoky - Silver Duckwings, coral breasted females at this time, lighter plumage, hoping to select these towards silver coloration without the robin's breast.
Birchen - still called Birchen (black chicks, black with white lacing as adult)
To be honest, with the above colorations and the variety reported to persist in the breed from the beginning, makes you think that they were wanting to create a breed with females like the silvers and males like the charcoals, which is likely why they never were able to resolve the mixed chick appearances.
Right now, we're moving towards Silvers and Charcoals to represent the breed, and working away from Birchens. The Smokys are a very lovely variety, and very likely will be worked with by interested breeders as well, and could be considered as another variety to pursue in the future. The Birchens are losing favor with many, as we try to move closer to the original image of the Iowa Blue.
I can't wait until we get to work on revising the standard to catch up with what we've learned, but we wanted to swap it out between show seasons to avoid confusion.