I use up bobbins left from quilting, the ends of spools, etc. The best match I do is dark colors on dark fabrics and light colors on light fabrics. For the most part, what you use for piecing is never seen and then I don't have all these half-used bobbins and spools laying around. (None of my machines is a picky thread user.) If I have used up my leftovers I use white or black. I mostly use C&C because I am cheap when it comes to thread.