In the early years of the breed through to the mid-20th century, Labradors of a shade we would now call "yellow" were in fact a dark, almost butterscotch, colour (visible in early yellow Labrador photographs). The shade was known as "Golden" until required to be changed by the UK Kennel Club, on the grounds that "Gold" was not actually a colour. Over the 20th century a preference for far lighter shades of yellow through to cream prevailed; until today most yellow Labradors are of this shade. Also fawn has been a common colour in the yellow lab variety.
A vigorous dog may or may not be high-energy, but everything he does, he does with vigor: he strains on the leash (until you train him not to), tries to plow through obstacles, and even eats and drinks with great big gulps. These dynamos need lots of training to learn good manners, and may not be the best fit for a home with young kids or someone who's elderly or frail. A low-vigor dog, on the other hand, has a more subdued approach to life.