When piecing light and dark fabrics together, what color of thread do you use?
 

So I've started a quilt that has some blocks all dark fabrics, some all light fabrics and some blocks are a mix of light and dark. I was using a cream Aurifil thread and when doing a few sample dark blocks noticed that the light thread was showing through on some of the seems. So it looks like I should use dark thread for the dark blocks instead of the cream. However, not sure what to use for the blocks that I will have a mix of the light and dark. What is best?

a medium gray might blend well on the blocks that contain light & dark fabrics- or taupe- medium 'neutral' colors often work well for both light & dark

I wonder if your stitch length is too long, or if your tensions are not properly balanced. Are you pressing seams to the dark side? I don't recall having piecing thread show even when piecing dark colors with off-white thread.

I agree with Prism. If the stitches are showing on the front side of your seams, that's a stitch length/tension issue, not so much a thread color issue. The only time piecing thread color should be a problem is if it shows through a light fabric before you even sew with it. I've pieced Kona solid black with white thread and it didn't show (any other thread color would have shown through the Kona solid white I was also using).

I use only 2 colors for piecing - a cream for lighter fabrics, and dark grey for darker fabrics. If I were piecing light and dark, I'd use the cream. I've not had a problem with threads showing in the seams. Could it be you're ironing the seams open instead of pressing them? And are you setting the seams before pressing them open? If you iron them, you take the chance of stretching the fabric too taut. Setting the seams first, then pressing them open should avoid that problem.

I am pressing some seams open to reduce bulk. I am making Ohio star blocks so on the hourglass block I am pressing to the dark side the first HST but when combining the second HST to make the hourglass I am pressing that final seam open. That is where I am seeing the light thread. I have a medium grey Aurifil spool but it isn't much darker than my cream so I don't think that will help much. I will look for a darker grey Aurifil to use for my mixed blocks.

yes, I like a neutral color as well.