So many wonderful suggestions -- you really can't go wrong with any of them. But I've got yet another!
I'd make a narrow pieced inner border with long strips of the brightly colored fabrics (varying sizes, but probably at least 8" each), followed by a larger solid outer border in either tan or dark brown (maybe with pieced patchwork cornerstones if I thought it needed a tie in). But I like bright artsy elements in my quilts -- I find them uplifting and cheery.