Any form of graduated change of state. Esp. visual. In particular in space as opposed to time (which would be transition). The spatial equivalent of this.\n> The [graduated tint] on those big (and invariably, coloured) sunglasses, popular in the late 1970s.\n> Numerous sunrise/set sky-scapes ...\n> 'The darkening sky set itself for a moment in a vast umberglaze from horizon to zenith as nighttime gently concealed a world and revealed a universe.'\n