hey tom, as i have trouble getting colored dyes in australia, i have always uses acrylics from the art stores..any good quality paint seams to work and there is a huge range of colors, lots of iridescents and pearescents and metalics, and if it is airbrushed on it retains the flexibility of the mask. I find i have to water down the paints for the airbrush but this doesnt seem to effect the mask. I use thin hat elastic for the masks. I would like to use leather but find if you want a good comfortable fit elastic is the way to go...i get it from sewing shops. I always put two small holes on either side so the elastic is double stranded and the two strands can be separated with one worn high on the head and the other lower.
I get a spray sealer from the craft shop, you can get matt or gloss, it protects the paint and leather, but i encourage mask wears not to get the mask wet if they can help it.