On the eve of World War I, Guillaume Apollinaire announced the birth of ‘pure painting’. Scholars have typically understood this as an early version of mid-century theories of abstract art; however, that interpretation ignores the poet’s close association with Robert and Sonia Delaunay. Those artists were deeply influenced by M. E. Chevreul, a nineteenth-century colour theorist who showed that complementary hues appear more pure when seen simultaneously. Most often discussed in relation to the phenomenological changes that occur when red and green are viewed side-by-side, simultaneous contrast suggests an alternative view of purity. For the Delaunays, pure painting was not a retreat from the world, but a way of making its dichotomies and conflicts more visible.