What name is given to a commedia dell'arte character who wore a diamond patterned costume?

The name you are looking for would be Arlecchino. Although, in traditional Commedia he does not wear this particular costume at all. He is just another servant like all the others. The mask of Arlecchino wears the diamond suit in the tradition of the Italian Carnevale. In Commedia it all started after Commedia DELL'Arte emigrated in France and with Goldoni.