I agree with Prism. If the stitches are showing on the front side of your seams, that's a stitch length/tension issue, not so much a thread color issue. The only time piecing thread color should be a problem is if it shows through a light fabric before you even sew with it. I've pieced Kona solid black with white thread and it didn't show (any other thread color would have shown through the Kona solid white I was also using).