First of all leg color has nothing to do with eggs color, the only physical feature that is associated with eggs color are the pea comb and earlobe color and they are not 100% full proof, just associated. Frequently pea comb birds lay blue/green. For the ear lobe if it is white the birds usually lays white and so on. The one exception to this is the Brown Leghorn. Leg color is associated with skin color. If the bird either male of female has yellow skin it will effect the color of the legs. If a bird which has blue slate legs is mated with a bird who has yellow legs or has the gene from somewhere down the road, the chicks would have greenish legs as the blue and yellow genes will mix and make green.
All this is rather complicated and this just touches the surface. I usually just wonder if the legs are true to the Standards for that breed. And since there are no standards for EEs, I usually do not think about the leg color. I do prefer slate, black and green. I like dark colored birds also. Eggs are fun when they are all colors.