The male Banded demoiselle is very striking and familiar, with its electric blue body and dark patches on each wing that catch the eye as it flutters. The female is probably less well known. Here's one demonstrating the full emerald green bodywork and wings. There were loads of males and females as well as other species fluttering around the site in the sun today, particularly by the low bridge by the spit.
I didn't get such a good photo of the male, but I include it for completeness. I suppose it's kind of arty!