Originally Posted by
loisf
I have four Aurifil 50 weight threads that I use for all piecing - white, black, grey and tan. It makes thinner seams that iron flatter than the heavier threads. I love it. Truth be told, I'm sure you could choose either the grey or tan and piece everything with it, but I use a lot of white or black sashing and backgrounds, so I perfer the white and black too.
I have the same 4 colors although I use mostly gray. However when I first started piecing (after years of other sewing) I used up most of my colored thread - not matching them to the fabric but just using them up.