There is not a formal recommendation for a 100-year anniversary color. Typically, wedding anniversaries are marked by colors up to the 75th anniversary, but after that milestone, there is not a guide.
Because of its regal nature, purple is often embraced by corporations to celebrate the centennial milestone. Also, diamond white is used to mark both the 60th and 75th wedding anniversary and is seen as a meaningful color that celebrates a big milestone. This is why it is often seen at centennial celebrations, according to Reference.com. Stemming from this theme, the diamond is frequently suggested as a symbol or a gift that appropriately marks the big occasion.