I use Bottom Line for most sewing : machine, hand and hand applique. pale green and pale blue (as I have alot of it) for everything, very thin, doesn't ever show
http://www.superiorthreads.com
When I want all cotton I use Aurifil - I have alot of it so can pick a colour. If I didn't, I'd stay with beige/cream or light gray for light and any dark colour for darker needs.