Thank you all for your suggestions. I appreciate the help. Gives me lots to consider.

I think I would use a batik also. My first choice would be something like the coral/orange color, and second choice would be one of the watery blues or greens. If you use the orange, I would bind in the ruddy Crimson color near the top right block.

What color thread will you use for the quilting? And do you want the quilting to blend with the backing or stand out?

I choose backings a little differently. I first ask myself if I want the quilting threads to show on the backside or if I want just the texture of the quilting to show more than the threads. So I consider what color thread I'm going to be quilting with before I choose the backing. Just my thoughts, but I would probably pick a peachy color solid or marble backing and binding; a peachy/coral color thread to quilt the sashings and coral/peachy blocks; change to a medium pink/fusha thread for some of the blocks, a medium green thread for some of the blocks; a medium navy blue for the remaining blocks. Or if I were quilting an edge to edge pattern I might choose a dark burnt orange thread top and bottom. Just my thoughts.

I wonder if the batiks would be stiff and, since it's backing, do you want to go to that expense? I would probably look for something such as what you have used for the sashing. Someone else has suggested a marble and I like that idea but staying within the same color as the sashing. Will this have borders? This is a beautiful quilt!

Certainly any of the block colors from the front would be nice. I, like Tartan, would coordinate the binding with the backing. I would also consider what you plan to do for the quilting because it is going to dominate on the back if you use a solid or near solid whether it is batik or other fabric. It will offer opportunity for really beautiful quilting.

Beautiful - I also agree with the darker blue for the border.

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*** I like the beige between the squares.
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*** Beautiful quilt.
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Me? I'd pick one of the dark fabrics.
Learned the hard way to not use stripes, etc. If it's "off " just a little bit, it makes me crazy.

Fabric.com has a wide variety of wide backing fabrics to choose from, one of their batiks would be great for your quilt.