Black Lab has issue with my friend

Question
My male black lab is about 3 he's neutered.  He's exceptionally friendly, when we got him he was not socialized and left in his previous owners backyard all day.  Now he's with us and has two other dogs to play with all day.  He used to be afraid of meeting people, now he's the complete opposite, he tends to be a bit too exuberant about it now.  

However, my friend is here for a visit and my black lab will sit and growl at him.  We admit its a bit ironic b/c my friend is black.  It seems silly but he's only growled at our friend and the only thing we can figure is that he's sensitive to race.  Which sounds absurd but we can't figure anything else.  

Answer
Unfortunately it does happen.  I often think they are reflecting their owners attitudes.  Since you are entertaining a black in your home, I doubt it is your fault, likely more baggage that came with him.  Go back to what you did with strangers at first, remain calm, greet the person warmly, have him give him treats.  The black man needs to remain calm too.  The dog will pick up any stress and add to the problem.  The other thing is leadership.  If you are in charge, the dog doesn't need to take it on himself to warn people.  

The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/ For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm