All Leghorns *should* have yellow legs. I have some white Leghorns with pink legs, as they've been selectively bred (not by me) for maximum egg production and not leg colour. They horrify serious Leghorn fans, but as utility birds they suit me fine as they're by far the best layers I've ever had. Paired with the correct leg colour roo, you could probably breed yellow legged offspring from your pink legged Exchequer quite easily. I'm not certain on this though as the genetics of it is something I'm still struggling to understand.