It's actually better to go with the darker color when you are given a choice of two. I'll choose the darkest grey or taupe I can find that matches the darkest color in the pieces (unless the darkest color is a tiny print, then I match the predominant color). The reason is that that the darker colors will not show as much, they'll get hidden in the "shadow" of the seam edge. I know it sounds illogical, but try it.
The only time I would piece with white is if I were piecing two white fabrics, and that just hasn't happened yet!
That said, yes I have quite a bit of white in my thread collection. Why? Because I too was taught to work with white
