Well there are all sorts of semantic issues here.
If it is totally dark in my room, I can’t make it more dark. If it is light in my room, I can make it more light.
But if it is light, and I turn off the light source, the boundary between light and dark travels at c. Indeed, if I turn the light intensity up or down, the boundary of the change travels at c.
The question does bring to mind the phenomenon of psuedo-particles. Probably the best known being the electron hole. In a structure filled with electrons, does the space where one could have been behave like a thing? The answer is that it does. With remarkable accuracy too. Right down to important quantum theory properties.
Then one could you ask. Does the Casmir effect count as a kind of special darkness? Here we have done the seemingly illogical. For a certain set of wavelengths, the space is actually darker than dark. It would still be limited to c.