the speed of dark is the same as light. in other words if your in a room without any light source except a litebulb and you turn that lightbulb off, who fast does it get dark? the absence of light travels at 186,000 miles per secound. unless your watching a sunset! and like a refridgerator, cold is the absence of heat. your refrigerator doesnt make the milk cold. it extracts the heat from the milk.
But is it arriving as particles (photons) or as waves (setting up interference patterns)?
Is its speed the Universal Speed Limit? I read Hawking one time (until my brain froze up - then I got out my 'Calvin & Hobbes' collection (excellent Xmas gift - the collected set, retail $150, but I've seen it for $99) and thawed my brain), and learned the following [caution - Brain Freeze Zone]:
If you have a molecule of Oxygen (or Hydrogen or any two-of-the-atom molecules) - O2 - the atoms spin in opposite directions (up or down). But the direction they spin is totally dependent on the observation, i.e., one time it's spinning up, the next instant it's down (feeling frosty yet?).
BUT . . . (insulate brain immediately), if you separate the two atoms and move them to opposite sides of the universe (roughly 35-40 billion light-years apart, I seem to remember), and observe the spin of one of the atoms, its twin will always be the opposite, SO . . . (owww) if you observe one up, the other will instantly be down. How is this 'communicated'?
Now build yourself a quantum computer, the one that uses the quantum levels of atoms as its 1s and 0s, and use the spins as your binary data, and your computer can transmit information across the universe INSTANTLY (OWWW!). How's that for busting the Speed Limit? ["How fast was I going, Officer?" . . . "Uh, infinity."]