If he wants an orange solid back, maybe he'll go for a mottled orange back. That will help hide the stitching on the back. I prefer to have darker colors on the back, meaning anything darker than white. I want something where some dirt won't show. So, I also do not like too much white on the top of a quilt, nor on borders or binding. Even Cream is a little light for the outer borders, backing, and binding as far as I'm concerned.
Orange should work fine for the backing. You may be able to use an orange varigated thread on the top, and the same or solid orange thread on the bobbin for the quilting.