I recently started having problems with UV mapping. I map the object on the same color yet it has different shades of the color. For example I was mapping a car I'm making for a game and it looked like this.
Try pressing (Ctrl+N) in edit mode of the mesh while all the mesh is selected, that will recalculate all the normals, also very important press (T) and in edit mode of the mesh while all the mesh is selected find button Remove Doubles. If non of this work try unwrapping the object again.