Labs come in a myriad of shades, from Black, to Chocolate, to Yellow. Of course, there are various hues in between, as yellows can range anywhere from white to fox-red.
Fox red Labradors are not a separate color category, nor are they rare; and thus they should not command a higher price. The same goes for whites. They are all Yellow Labs, just at different ends of the color spectrum. Either shade will still be registered with the AKC as "yellow."
I personally LIKE to see the variety of yellow hues, but beware of breeders marketing those dogs as "rare," and charging an increased price based on color alone. I have nothing against "silver labs" (aka "Weimradors") but I do not consider them Labrador Retrievers due to their mixed heritage.
A Black Lab
Photo coutesy of Servant's Labradors
A Yellow Lab
Photo Courtesy of ArrowHead Kennels
A Chocolate Lab
Photo courtesy of Nala
A Fox-Red Labrador
Photo coutesy of Servant's Labradors
A Creame Labrador
Photo coutesy of Servant's Labradors
A White Labrador
Photo Courtesy of Yellow (Blond, and yes White!)
The Elusive "Silver" Lab
Photo courtesy of Christ Culo Kennels
So far there haven't been any "blue" Labradors noticed yet, but as the popularity of this breed continues to increase, I am sure we will see a rise in these other colors. Again, beware of breeders with a rare or unique lab coloring -- at a high price.