Because a person cannot celebrate a hundredth anniversary, merely a hundredth birthday, and only something like a company or country can celebrate a 100th anniversary there are no gifts or colours associated with this.
It would be possible to celabrate a 100th aniversary, although I admit not likely. People have been recorded to live to 120+, if they married at 16 then they could have a 100th aniversary. Ta Hamish.