Many artists and scientists - including Buffon, Goethe, and Philipp Otto Runge - who observed the vividly coloured shadows that appear outdoors around dawn and dusk, or indoors when a candle burns under waning daylight, chose to describe their colours as 'beautiful'. Paul Smith explains what makes these ephemeral effects worthy of such appreciation - or how depictions of coloured shadows have genuine aesthetic and epistemological significance...