For continued good health, we are urged to design our meals around the colours of the rainbow. To answer the question "Why?" requires consideration of two evolutionary stories. These broadly are natural evolution, and evolution driven by the activities of human beings. For the first, we need to go back to the start of life on earth and think about pigments rather than colour. There are two major pigment families, carotenoids and those based on the porphyrin ring, without both of which life on earth would not exist, and which still play major roles in our make-up and well-being. Other pigments, edible and poisonous evolved as pressures on plant life increased through predation and their own need for survival. The second story commenced with the arrival of human beings and their eventual ability to control fire leading to development of food preservation, processing and more recently, ultraprocessing. The rainbow rule does not apply to such foods in which colour is an indicator of process. Heavily processed foods include use of coloured, cheap, poor quality, and unhealthy ingredients contributing to the present health crisis. For this intervention by humans we must switch from consideration of pigment to that of colour, because it is colour that is a major factor in our selection of the food we eat today.