I like using the same color top and bottom no matter what the backing fabric is cause I find the quilting looks great on the back and you can see it much better as there's no various blocks hiding the lovely quilting. This way both sides look great but that's my opinion. On one of my quilts, the recipents loved both sides and didn't know which side they wanted to face up for all to see. I normally try to match up my backings with the quilt itself though so most times the thread looks good anyway.