Pick a solid color or small print that blends with the front. I would not use a white or cream. I like for the backing to be a surprise.

I love your batik quilt, colors are beautiful and great pattern... I am finishing up a queen size batik for my son but I chose 108" wide neutral batik for the backing as I wanted it to "wear" the same. I think you would be happier with a matching batik for your lovely quilt rather than muslin.

I would search for a simple solid in one of the medium tones of your quilt. Some one mentioned the sea foam green and the would be fine. I would not choose the darker colors because the contrast would be "too shocking". The soft lavender would work too. I often use a white on white for the back but it can depend on who the quilt is for and how it will be used.

I like your border. I always like that half hexie but never think of it when doing my own! Silly me.

I personally would not use the flannel, for all kinds of reasons beyond the color. Just my opinion.

thank you all for you comments and I agree with those of you who suggest using light green or violet for backing or even a 'mottled' color, it will help hide imperfections in quilting which I will be doing myself on my Juki.

My sister buys a lot of tone on tone white and off-white. I shop at her house all the time. It goes with EVERYTHING.

That's a beautiful quilt. I use flannel all the time as many of my recipients appreciate the warmth. I always pre- wash it and so far, I've heard nothing but good results. I, personally like flannel. Makes for a nice cuddly, warm cover.

I have made this pattern too - it was very fun and easy - as for the backing - if you watch online you can get great deals on backing fabrics. Fat Quarter Shop has a daily deal that last for 24 hrs - usually the yardage is around $ 4.30 yrd or so or check fabricshopperonline.com - they list fabric deals usually on Saturdays from all over the internet - also I have found many great deals on etsy - just start searching for quilting fabric or specific colors - you will be surprised. I love your quilt, by the way, one of my favorite colors.

One more thing, try Craftsy, they often have great deals on fabric yardage and I have seen many Batiks on the site too - check back often with them.

Your quilt is beautiful! For backing its often whatever there is enough of in my stash.
Batiks can cause problems with stitch quality because the fabric has such a high thread count. Good quality flannel makes a very nice backing, it stays on the bed better too.
Sharon in Texas

Have you thought of using a light green flat sheet for the backing?

I didn't read all comments, but make sure if you use flannel on the back to wash and dry it two or three times because of shrinkage. Love your top and you don't want the back to ruin it. Good luck.