Ever since Newton's groundbreaking work on the composed nature of light, additive colour mixing (and its laws) are subject to the interest of physicists as well as other sciences. In this paper, we present a setup for simple lab or home experiments on additive colour mixing and the laws of colour mixing. Students use the screen of a laptop or handheld device as (coloured) light source for respective experiments and can directly inspect the results of a superposition of different colours. With basic skills in designing presentation slides students can autonomously implement mixing experiments and explore the secrets which inspired GraBmann, Maxwell, and others.