Like many other black lab owers, I am questioning the white fur patches that my lab has. He "Iverson" has a patch on his chest bone and on the tips of his back paws. They are small patches but nono the less I too thought that black labs are to be completely black. Also he has turned a year old on the 7th of July and to me he still doesn't look full grown.
A small white spot on the chest is permissible in the breed standard, so don't worry about that. Many labs from working lines have white markings on their feet. An interesting site for colour variations in labradors is here.
Jeangenie, in your link, the yellow puppy eating from the blue bowl has a perfect musical note marking in black on it's coat. I don't suppose you know what he ended up being named, do you? Something musical? Just curious.