My favorite thread is Aurafil. It's hard to lay out $10 for a spool but they last forever!!! It is also not the easiest item to find and when I do, there are limited colors available. But I can find grey, cream and white quite easily. For piecing I use grey primarily but with lighter fabrics, I use cream and white. If I'm sewing on a border of something like solid black or red, I do try to match the color as it seems to be more evident in borders than in piecing.