Always check to make sure your dogs aren't digging to freedoms or their friend's yard. Place a rock over the hole when you fill it in or think of cementing the boards or even cinder blocks can keep those pups from returning to the scene of the crime.
This is cute. But genetically speaking, labs can have any color puppies (black, chocolate, yellow) regardless of the color of the parents. So yea it's strange for a yellow lab to have all black puppies, but not unheard of.