Seems like a simple enough task to choose a thread color for making a quilt. That is until you choose the wrong color and it becomes painfully complex to deal with. The navy thread looks like black next to the white. The orange thread peaks out between the pieces. The pale pink thread looks white next to the darker pinks. Here are some guidelines that we’ve developed over the years that may help.
For piecing, “Split the Difference and Blend.” Choose a thread that is halfway between the lightest and darkest fabrics in the quilt. If you have a multicolored quilt try a taupe or gray thread. Look for the most neutral color you can find and look at a single strand of it on the fabric. Remember that thread looks very different on the cone than it does as a strand. Bear in mind that fabric often looks darker once stitched so test a few on scraps before you commit to the whole thing.
For quilting, think about the role of the quilting. Should it contrast with the fabric to add visual interest? Would you prefer that it disappear because the piecing or fabric is visually complex? How about the backing? How will it look on the back? When machine quilting, some people advocate using different threads on the back and front. I think this works if they are pretty close in hue or value but I’ve had really bad results if they’re too different. It can look really messy as every little change in tension and be distracting. If you have big areas of a single color you can switch threads as well. Many of our quilts have long thin (less than an inch wide) elements in them of contrasting colors. I frequently leave these unquilted.
Consider also the difference in the fiber content of the thread and how the thread is going to lie on the fabric once quilted. Cotton threads tend to be thicker than polyester blends and make the quilting more obvious. In general I match the fiber content of the thread to the fabric I’m using, so I generally use cotton thread for all piecing and quilting. Sometimes, however, I just can’t find the right shade in cotton and I piece with polyester, but it’s not ideal.
Before you make your final thread choice, audition a thread color that you would never have thought would look good just to see what it would look like. About seven years ago someone rented our long-arm quilting machine to quilt a quilt with peacock blue and green fabrics. She chose a golden yellow that I would never have chosen, but it looked fantastic and totally transformed the quilt.