I recently purchased some of the matting for making new seals on several Bren mag tins and the only stuff that I could find is black in colour but does comes in various widths and thicknesses. I also got some of the same but thinner matting for the top seal of the Bren Transit chest. I got my supplies from Paul Beck Vintage Supplies if memory serves me correctly (other suppliers are available). I don't know if the matting that is available today and/or that I've used has ever seen a horse, probably synthetic.