Challenge them to mix brown and remember how they did it. Ask them to bring in green items and find and create a "green corner" - discuss which items have more blue in and which have more yellow.
KS2 Paste a photograph cut from a magazine onto a large piece of white paper and continue painting the landscape out from the edge of the illustration, matching the colours carefully so that the join does not show. Explore how one colour changes when painted on to different coloured papers. Look at the Pointillists and explore optical colour mixing using contrasting painted dots which merge when viewed from a distance.
KS3 Explore hot and cold colours. What is a warm green? Introduce the relationship between colour and emotion. Show pupils how Picasso's 'Weeping woman' (Tate Gallery) uses colour to reinforce the emotional charge of the painting. What colours do they associate with anger, sadness and happiness?
KS4 Show pupils the large collage of Matisse, 'L'escargot' (Tate Gallery) which consists of cut up pieces of painted paper. Then introduce them to complementary colours by looking at Bridget Riley stripe paintings and use the torn paper technique to juxtapose complementary colours in a large vibrating abstract.
KS5 Introduce the concept of tonal values and colour; challenge pupils to mix a red and green which have the same tonal value. Limit students to a basic range of primary colours to extend their colour use and understanding of a limited palette.