the white is the backing paper on the fusable strip . this is removed once you are ready to turn the bias over to iron in place.
if you want to do lead work on a quilt then choose a narrow black ribbon the same width as the fusable webbing and iron it on, no more guessing or holding it in place great to create letters or stainglass window effect. simply lay it down along the lines and press, done.
hope this explains things
annie in the uk