I made a YBR quilt all in yellows for my parents, so just one color in different tones will work fine. I think yellow and red would be lovely. Throw in a little cream color if you think it needs something else. To me, black would be too startling a contrast but then I personally prefer lighter colors. Please post when you're done so we can see how it turns out.
What a wonderful person you are to have taken this young man into your home when he needed a helping hand.