Choosing a backing when I can't match original fabric?
 

https://imgur.com/3zvbFPFI'm in the final stage of assembling a quilt (photo attached, don't mind the truncated points, I'm kind of new at this!). I'm now realizing that I won't have enough of the main solid fabric to make the backing as planned. Problem is, I can't for the life of me remember where I got it! Been through every receipt and order summary and I can't find it. The "triangle" fabrics were from the remnant bin. In normal times I would take a swatch to the fabric store and see if I can find the same color, but of course it's not clear when that will be an option. I find that blue and green colors are pretty tough to match from the computer screen. Should I put this one in the WIP pile til I can shop in-store? Would it look okay with some sort of neutral color, maybe gray or navy? Thoughts appreciated.

I agree using a print fabric on the back. It will compliment the solids on the front. You should easily be able to find fabric with the tones of blues you have in the front. You don't have to have but one of the blue colors in the print to have it work well.

There is no rule that says you have to use the same fabrics front and back. 😉 I agree with choosing a print for the back; if you select a busy print it will be harder to see any wobbles and goofs in the quilting.

I try to find in my stash something I like with the front fabrics. Or I pick a tan. off white or something that will go with both sides.

I hardly ever use a backing fabric that is the same as one on the front. I hate piecing backings (don’t judge), so I almost always find a wide back fabric that coordinates. There are lots of mottled prints that goes with a wide variety of fabric.

I agree with the others. You could find a lovely print to coordinate with it. I don't think I've ever matched the front and back.

I also use different backings that coordinate. Go for it!!

If you have enough fabric to bind the quilt that matches the front I wouldn't worry about the back matching the front. I usually like the wider fabrics too for the backing, so my concern with the back is that it coordinates with the binding. Since I like to see the quilting, sometimes I put the quilt with the backside up.

Since the triangles all all different colors, i think the back could be any cool blue/green color.