Since the Renaissance, artists have known that by combining red, yellow and blue, they can generate a wide variety of colours. By using pure primary colours, as Piet Mondrian did, the aim is no longer to reproduce the world or mix shades, but to assert colours recognised as fundamental in art, science and industry. Red, yellow and blue thus become signs, conveyors of a universal visual language. The selection of works presented in this newsletter highlights this radical approach: compositions in which primary colours stand out for their intensity, clarity and expressive power, reminding us how simplicity can be a source of great visual richness.