Your quilt is really going to be gorgeous! Since you asked about that fabric being border, I agree that it's too busy for the butterflies --detracts from their loveliness. However, I think it would make a cool binding and backing.

Butterfly quilt will be stunning. But.....I agree that the circle fabric is too busy for this quilt. But I do like the new fabric. Too bad we don't have a Holly Lobby near me, I would like to purchase some it looks fun. BrendaK

Love what you did with your butterfly panels. Quilt will be stunning.

Love the quilt and the black setting triangles. I agree with the others that the border fabric would detract from the beautiful butterflies and flowers. I would try a blue or orange solid or tone on tone fabric.

I think it looks great.

if you make the border two black strips with a thin strip of your new fabric? can you lay it with the blacks laid over it either side and show us how it might look?

I'd put a solid sashing around the quilt before putting on the border, my teacher always said to truly enjoy a busy quilt you have to give the eyes a place to rest before adding a busy print. Adding a sashing around it first would do that.

I would add a wide black border the same as the background. This way the quilt top will float. Sometimes a print border doesn't add anything to the pattern.

Love the butterflies with a solid or tone on tone fabric but the colorful circles would make a great back if you have enough.

That is going to be one gorgeous quilt, but I, too, would choose a non-busy border as others have suggested.