Colouring Penrose-deBruijn tiles based on their shape and orientation can look very nice (I have an applet that does that: https://t.co/I3iY3hbE2D), but I only recently learned that they can always be 3-coloured, as shown by Sibley & Wagon 20 years ago:https://t.co/Fjw7fyTvHr pic.twitter.com/DIYorKdhzd

— Greg Egan (@gregeganSF) November 21, 2020