As a chemist, I know some things about the uses of various chemicals - found at a supermarket - that are not listed under 'Common Uses.' Such little nugget's as making an excellent, non-toxic metal-polish from grape-juice. Many others. 3% H2O2 ( hydrogen peroxide) is often used my stamp collectors to restore postage stamps that have faded in color due to exposure to sunlight.

Try it.

Another solution is using leather-dye - available at leather-goods stores. But be very careful - these contain aniline-based dyes. Very toxic and may cause cancer.