Hate to put a spanner in the works, but in my experience there IS a difference between colours, especially when it comes to working Labradors.
I have found that most of the chocolate Labs take a bit longer to 'grow up' than the Blacks and Yellows, probably due to the fact that a lot of people were breeding for the chocolate colour, rather than the working ability. This also meant that up until recently, Chocs tended to be physically larger, especially the dogs.
This is slowly changing and you can now find some good working chocolates, but you'll need to do your homework.
Best of