'Colour based on nature' takes the concept of Irma Boom's previous work further afield, highlighting UNESCO World Heritage sites across the globe and on every continent. This time, the colour diagrams are derived from 80 natural locations designated by the UNESCO list. It is an exercise in describing without words, using instead colours to evoke and celebrate the essence of a place. Detailed information about the World Heritage properties, their selection criteria, how many are inscribed per nation and in what regions such sites are most endangered makes this an important tribute to the reasons such places exist.