Abstract: A coloring agent, preferably metallic particles, is disposed in a solution that contains unvulcanized diene rubber(s) and a rubber vulcanization accelerator. Crosslinkable silicone and/or modified EPDM may also be disposed in the solution. The coating material is substantially free of free sulfur, and preferably is also substantially free of carbon black. The accelerator scavenges sulfur from a vulcanized rubber substrate to auto-vulcanize the rubber solids, and any crosslinkable silicone and/or modified EPDM present. Coating materials that do not contain any coloring agent are also disclosed.