In the late 1960s early 1970s, Ben Hartley's concern shifted strongly in the direction of colour. He was especially drawn towards the range of joyous vivid colour in the work of Bonnard. The writings of Matisse, in particular his notion "Plus c'est plat, plus c'est de l'art " (The more it is flat, the more it is art) were also important. A simple change in the use of gouache brought about a major change in the appearance of the work. Instead of applying the paint directly onto the brown paper, a white undercoat was first applied and the work became vividly bright. At the same time the approach to space becomes totally liberated. Whilst adhering seriously to the theories of the Modern French School, Ben Hartley gave rein in his new work to his love of humour.