Welcome from Ontario, Canada. It's beautiful! I would think it would depend on how it is pieced. Did the coloured pieces go down onto a background fabric with a fusible and then fusible leading on top? If so then it could be quilted in any manner you wanted but stitching on the leading would be my choice. I think I'd use black thread on the black leading.
If the pieces are not fused down at all, I think I would top stitch the leading down with black thread first to secure all the pieces and then layer it to quilt. I hope you repost it when it's done, it's going to be awesome!