I noticed my chocolate lab has two different shades of brown.  
In the summer, she turns a really pretty golden brown.  Although it is partly because of the sunshine lightening the tint.  Recently her winter coat has been coming in quite a bit darker than the summer coat.  Really shiney, she has a beautiful coat.  You can easily see the difference as there are a few spots of summer lightness around her shoulders.  
I bathed and brushed her once since she started shedding for the winter coat (weird).  It seems I caught it at the perfect time - her fur is great now.  Her shed cycle must be complete.  When she was in the tub, a lot of hair came out and thats all she needed.