Purple rain, purple rain... It doesn't matter if you're more of a Michael fan than a Prince fan, we can unanimously agree that this is a brilliant song. Above all, it succeeds in making us love purple - a powerful, esoteric, hypnotising colour. This colour, which has long been the prerogative of royalty and religious powers, has come back into favour in recent years, in art, design and architecture. From the most discreet mauve to ultra-violet, our artists are sprinkling their works with touches of violet. Discover them in this week's selection.