What color thread do you use if you are sewing blocks very light and very dark?

I usually use a gray/green, or gray. If it is mostly black I will use black. I don't usually by thread to match for piecing.

I always use a neutral for all piecing.

I use light beige or dark beige.

Neutral, grey or beigeish

I use a neutral cream for 95% of my piecing.

Neutral cream, or gray, for me too :)

Thanks that is what I have been using, natural so maybe I am doing it right!!

neutral is good

i try very hard to use leftover bits. so if i'm sewing reds, i'll use up orange thread. if i'm sewing dark blue, i'll use up purple. like that. otherwise, either dark or light grey. plus white.

EDIT: my leftover colors are from garment sewing.