As a fairly impoverished Photography student (subsisting on a much-too-tight Allowance!), I once made my own bellows for an ancient mahogany technical camera.
They were made from brown paper with cardboard stiffeners for each pleat. Black fabric formed the lining and I painted the exterior with several coatings of black latex paint. Those bellows were entirely light-tight and functioned perfectly.
I can highly recommend black latex paint for bellows renovation.