Hi Sugarplum,
Wonderful wisdom has already been shared as well as your own insights. I am just agreeing. I know when I decorate an easy trick is picking something I love, a piece of art or a cushion, and pull all the colors from it. After all, I already love the combination and a gifted expert combined them! So I think you're brilliant to take your colors from your favorite shirt! Now, about that mustard yellow, have your considered caramel leather boots, shoes, belts, purses? Black and caramel are oh so elegant. Happy decorating - yourself that is!