Meet my half @ssed duns (joke, I know that they aren't dun)
Bay Thoroughbred mare:
She even gets dark shading on her face for a couple summer months.
Her half sister, a black bay sabino:
And their half brother, a buckskin (I am surprised but I do not have any good photos of his counter shading. He is just as prominent as his sisters.)
What causes counter shading? Is there a genetic reason for it?