Yes but you have to be sure to use a slate legged parent in every mating. Doesn;t matter which sex the slate leg is- slate leg roo, willow leg hens or willow leg roo with slate leg hens are equally "good" for producing slate leg offspring(in both sexes as it;'s not sex linked either).
Creating a line pure breeding for slate legs is trickier though.. as you cannot tell visually which ones are pure slate or green carriers. The most straightforward way to do this is individually test each bird by breeding it with a yellow or green leg bird and try to hatch 10 chicks at least. Any yellow/green leg chick, even if just one proves the bird being tested is a carrier. Then you decide if the bird is worth breeding or to take out of the breeding pool. Most breeders don't go this far though.. breeding slate with slate will produce mostly slates even if they are both green carriers.
You're gonna produce a beautiful line with those birds.
