I don't know who the dark skinned man on the bill. That being said, his skin color is intentional. The shadow claim is silly for obvious reasons.
Also, those who says its John Hanson, I see their point. John Hanson was a Moor. The Moors originated from Africa. IF that is John Hanson of course he would be depicted as a dark skinned man or Black. Now, why would he be there? It is (or should be) common knowledge that Gen. Washington worked with the Moors during the revolution, FACT. There are even numerous paintings of Gen. Washington with Moor 'consultants', FACT. My advice, go to your local library (not Wikipedia) and read some actual books. You'll find out more about the Moors than you would ever think possible (mind blowing stuff!) Folks, they can't hide everything and they don't need to. The history is there, just read it and inform yourself. If you're looking for a starting point, let me know.