Sonia and Robert Delaunay often used it within their work, as does David Hockney and although I can spot it on the colour wheel I'm still clueless as to what it's actually called!

Vivienne Westwood: Anglomania dress
Priestly's Vintage: Deb hat
Holly Fulton: Deco necklace
Dries Van Noten: Fall 2010 ready to wear