The only info I've been able to find is that it would disqualify him from showing if he's not solid black. Any combo of colours is a disqualification, but I don't think it neccesarily means he isn't pure-bred.

Another thing I would consider, is that chocolate labs range from very dark brown, to a lighter brown..maybe you've been douped and you have a chocolate lab with shading variations??

I also found an article that said ocassionaly breeding two black labs will result in chocolate or yellow labs, they're not always guaranteed to produce black puppies. So that may be a possibility in your case.

Hopefully someone with better knowledge than a few internet searches, can help you out a little more.

I thought I adopted a pure black cat, but she's actually orange and brown in the light! Looks can be decieving somtimes :)

I've seen photos of black/brown labs in breed quizes.

I couldn't find any pictures, but here is the breed standard for color

Color
The Labrador Retriever coat colors are black, yellow and chocolate. Any other color or a combination of colors is a disqualification. A small white spot on the chest is permissible, but not desirable. White hairs from aging or scarring are not to be misinterpreted as brindling.

Black - Blacks are all black. A black with brindle markings or a black with tan markings is a disqualification.

Yellow - Yellows may range in color from fox-red to light cream, with variations in shading on the ears, back, and underparts of the dog.

Chocolate - Chocolates can vary in shade from light to dark chocolate. Chocolate with brindle or tan markings is a disqualification.

Is he outside a lot? Sometimes the sun will turn a dark coat a rusty color. Also could be where he is licking and those areas are saliva stained.

Lisa

Maybe he's just shedding his baby coat and the dead hair looks brown. My black and rust minpin is ordinarily jet black, but he can get a very distinct brown tinge when he's shedding.

Black and Chocolate lab coats don't change colors.

Yellows get a bit darker as they get older and lose their puppy fluff. I know alot of black labbies and they were black when they were puppies, and they stayed that way. Of course, they get gray like all old dogs. The sun will not lighten the lab's coat.

It sounds like this dog is getting the classic black and tan coloring you see in Dobermans, Rottweilers, Minpins, Manchester Terriers and a hundred other dogs. My friend's mutt is black with the slightest tint of brown in these classic areas. Can you ask the breeder if any of their other black dogs have this?

Were you planning to show or breed this dog?

If not, I wouldn't worry about it...
Get him spayed so as not to pass on the trait.

No, we're not planning on showing or breeding him. The only competition we maybe planned on was agility competitions and maybe the doggie long jump. We're not worried about it, I just in all my years had never seen this kind of coloring. I will say that his Dad was chocolate and his Mom was black, but she did have a little brindling on her chest, so maybe he is getting some chocolate coloring from them, and it's just now showing up? You know something interesting, the brown tint shows up only when he is outside with the sun shining on him. When he's inside or it's cloudy outside, you would swear he is jet black. Interesting, huh?