Darkness, the polar opposite to brightness, is understood as a lack of illumination or an absence of visible light.
Humans are unable to distinguish color in conditions of either high brightness or darkness.
There is no such thing as darkness nor cold.
Darkness is the absence of light and cold is the absence of heat. So you can't "see" darkness, only perceive it as there is no light.
Most of us already know that darkness is the absence of light, and that light travels at the fastest speed possible for a physical object.
So, what does this mean? In short, it means that, the moment that light leaves, darkness returns. In this respect, darkness has the same speed as light.