The model P was influenced by Colt's earlier designs, even though he was gone when it came into production. The gun was definately a left handed design. The guns were designed to be used by horse mounted soldiers, and if a soldier was bouncing along on his horse, he certainly didn't want to have to switch the gun from his strong hand to his weak to unload, then reload, then switch back.

Since most people are right handed, a right handed gun would have had the loading gate on the left, which would keep the gun in the strong hand while loading with the weak, or off hand.