A classic boater in Milan straw trimmed with a navy blue silk ribbon and the appropriate for women. 
For men we usally substitute a black or striped band. 
At the Turn of the Century this was the quintessential hat for gentleman in the summer.
Women beggin to wear more sportswear and adopted mens' hats as their own. The boarter was reborn in many different proportions and trimmied according to the style of the lady wearing the hat.