Marvel did a mini-series a couple of years back, called TRUTH, I believe. It basically revealed that the first tests the US government did for the super-soldier formula were made on african-american men, therefore the first Captain America was, in fact, a black man. Even though I haven't read that series or the Young Avengers, I believe the kid who is Cap's equivalent on that group may be a relative of that first super soldier. Please feel free to correct me on any of this if I'm mistaken.