Green Sky, Blue Grass - this title is perhaps irritating: isn't the sky blue and the grass green? In ancient Japanese poetry the sky is sometimes described as green, and the grass as blue. Even though all people see the same way, physiologically speaking, colours are perceived differently, and in various cultures they are ordered according to different criteria. In addition, many diverse social and cosmological ideas are linked to colours. This publication sheds light on the phenomenon of "colour" from interdisciplinary perspectives. Anthropological case studies enter into a dialogue with essays from the fields of philosophy, linguistics, and physics.