Very frequently, I piece the backs of my quilts because I am truly insistent upon using only from my stash. Here is the address to my facebook pictures of my quilts if you want to see:

https://www.facebook.com/media/set/?...2702514&type=3

I was going to recommend this too!!!

I like to use up what was used for the front. Then add too as needed.

I lay the front down and start putting pieces on top until its big enough. Then start sewing together, adding a strip of squares/triangle/single piece to make them fit. Can use up scraps this way also. Sometimes the back is as pretty as the top because I was more creative.

I was thinking that if you could find a print with your colors in it, you could place that strip down the middle and use that fabric as the binding. That would tie it all together and maybe be an interesting effect.

Suggestion: a square in a square. Or, my first thought was large stripes using up the black, but if not enough lengths, join with an angle creating a pattern. Consider this an opportunity to express your own style.

I was thinking a big square/rectangle from the black centered in the back, with a single color surrounding it, although you could surround it with different colors.

I have only done one pieced back and it was not a problem. I had a fabric that I was in love with for the back of a quilt, but not enough for the whole backing. I cut the fabric in 10.5" squares and pieced with alternating solids. The 10.5" size is a suggestion on the Quiltville website. The quilt was a gift and the pieced backing was a hit with everyone. I am getting ready to do a similar back on a postage stamp quilt I just finished piecing. I went to JoAnn to find backing and was so disappointed in their stock and quality that I came home empty handed. Good luck. I know you have gotten a lot of great advice here.

Gosh, there are so many great ideas to choose from! Well, I have jumped in and started the back. I'm using the four patch idea. Kinda sorta. I'm using my remaining black, and for the "second color", I'm piecing stripes. Oh, and I added a couple of vertical stripes. Well, I guess this will be my own variation. I'll post here when it's done! Thank you all for being so willing to help.

Please check with longarm quilter to see if she is prepared to use a quilted backing. Some refuse because the bulky seams break needles and cause problems, no matter how well pressed and starched. I did a quilt with what looked like a runner near the bottom using the same fabrics but easy pattern.
Good luck.

Welcome and your project sounds wonderful. Please post a picture. I love to see everyone's quilts.