What color thread do you use most often?

I always match my thread, but there is always a JoAnne's coupon for this. After a while you will find you have all the color you need or something close enough.

maybe the newbie in me but i remember reading and hearing that light grey works with almost everything as a blending color. i am using it predominantly in a quilt i am piecing and cannot tell at all. when it comes to binding the quilt i will most definately match what i am stitching around or contrast if it makes a bigger impact.

I use a lot of black and white but also a khaki color, can't remember the number, it's a warm gray/taupe color and blends well if I don't have a matching color. But I usually buy a matching color and now it's rare that I don't already have something to match in my stash.

If you don't have an exact match it's better to err on the side of a little darker or go with a gray that is a similar value (light or dark). It will hide in the seam. Hold the thread against the fabric and squint - if you can't see it, that's good enough!

I use black and white almost exclusively.  I only match threads for topstitching and then my bobin thread is still almost certain to be black or white.