There was just one constant in Hockney’s work: bold, life-affirming colour. David Lister looks back at the art the late painter has been creating since the 1950s D avid Hockney has been painting so brilliantly for so long that, looking back at his work across the decades, it can feel like one is looking at different artists and different people. The quietly campaigning painter of gay scenes in the late Fifties and early Sixties, when homosexuality was still illegal, seemed a rather different