In the late 1940s and throughout the 1950s Oliver painted in watercolour. Although entirely self-taught, the attention to detail, and his ability to wreathe a landscape in cloud or mist was remarkable. His watercolours were meticulously observed paintings, representational but by no means hyper-real. For many people, they are the works they still cherish the most. They show skill and integrity. Some of the watercolours have a dark tone to them: sombre mountains and black silhouettes of exposed tree roots. They are an indication of things to come.