I've been wearing my summer dresses more than any other item during the heatwave but co-ords are a chic alternative that I shouldn't forget about. They come in various forms and although trouser and top sets are most common, Harriet Phillips wore a stunning skirt and blouse co-ord to Wimbledon last year.
At the time she wasn't a Royal Family member and her style was a little more lowkey, though the colour is something she still wears a lot now. The Wiggy Kit Esti top and skirt were a pale periwinkle blue and had delicate white Broderie Anglaise detailing.