Sixty years of marriage is called the diamond anniversary. To coordinate with this name, the whole theme of this anniversary centers around diamonds. A diamond is the gemstone representing it as well as the recommended gift to celebrate it, although the star ruby is mentioned as an alternate choice.
Diamond white is the color for the anniversary also. The diamond, which often symbolizes endurance, represents the enduring nature of this long marriage. According to About.com, Queen Victoria's Diamond Jubilee, which took place in 1897 and marked her 60-year reign as Britain's monarch, introduced the tradition associated with a 60th anniversary.