Umberglaze

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.

The graduated tint on those big (and invariably, coloured) sunglasses, popular in the late 1970s.

Numerous sunrise/set sky-scapes ...

'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.'