A bunch of drawers that draw.
I found this to be a lovely video - shows colour and air perspective in a simple way. The commentary is in German (Austrian) but the words are superfluous for this demo. Given below is my translation of the information beneath the video.
How does a watercolour develop? Watercolour painting should not be difficult. Watercolour course and painting trips with Wolfgang Baxrainer at www.baxrainer.at