When I took my very first quilting class, the instructor said that the backing should not be any darker than the lightest fabric on the top owing to the shadowing. I have pretty much followed this advice. If you go darker, then be sure to audition your backing and make sure it does not shadow otherwise, go w/a heavier batting.

I have been shopping at mny stash. I have put pieced backings on the last three I've made. Almost like getting 2 quilts in one, and my stash is getting smaller.

I use a lot of large "pieces" ..... scraps if you will......I do somewhat coordinate them but not with the front so much,....more with each other. I also love to use flannel if I want the quilt to be a bit warmer and softer. Sometimes I coordinate extra blocks into the backing. I generally feel that almost anything goes as long as it doesn't loundly fight with the top.....now a special top is different. Then I do try to make a nice and somewhat coordinating choice,

Good advice from everyone. I frequently piece my backs and I don't usually use solid or dark backs so the color won't shadow through.

I've seen nice looking backs with a strip of one of the top fabrics or piano keys from the top down the center back or along the sides of the back, or you can use a coordinating fabric down the center back or around the sides.

I usually look for larger pieces of fabric in my stash -- if I have to piece it that is fine. I rarely buy fabric that "matches" the front. At this point I'm trying to use what I already have!

I tend to use fabric that I have had forever and have no earthly idea why I still have it. If it has the colors of the quilt top and compliments the quilt top then usually that is it. A big part of choosing is if I want my quilting to show or be invisible. For example, the quilt I'm doing now is primarily aqua so I selected a floral, pale, with shades of aqua as the backing. I am quilting using a varigated aqua thread and a geometric pattern, the back looks very pretty so far. I recently made a quilt for my son using his college logo fabric, with musical sashing as he played in the marching band and bordered it in black. I choose a red tartan plaid for the backing as to me it was in keeping with the fact that it was for a man. Then when I quilted it I used a gold thread and it made the back really pop. So I guess picking a backing is really just doing what looks good to you and compliments your beautiful work on the top. Oh, quality of the fabric is super important to me. I will not use a flimsy fabric for the backing. Hope this helps you a little bit.

backsidefabrics.com will send you free swatches of whatever you want to try out. All their fabrics are for backings.

I have...
Bought a backing to match the front.
Bought a white flannel sheet and dyed to match.
Pieced a back from extra front fabric.
Used the main front fabric as the back.

My quilts are "gifted hugs", so show quality is not important in my quilts. Sturdy is my main concern.

Most of the time my quilt backings are whatever I have enough of in my stash. It doesn't have to match the front of the quilt.
Sharon