I was reading a very interesting article on the origins of the Lab and the history of the breed. Duggan has the cutest white triangles on the back of his paws that can only be seen when he is standing and you look from behind. I kind of think I could use it as an identifier if he ever goes missing but wondering if this is genetic leading back to the Saint John Water dogs or if it might be a more modern mutation. Other than this he is a working line and all black.
Look up "Bolo spots". White marks on the feet are generally attributed to lineage dating back to the famous Banchory Bolo, who had these marks. Willow has a few tufts of white between her toes. I don't know if they count as Bolo spots!
Molly has these too. She's a cross, but her mother was a Chesapeake Bay Retriever, so I don't think the spots come from that side.