It was sort of like a "Spinal Tap" moment - colors combine differently depending on whether you are mixing light waves or formulating materials. Combine all the colors of pigment and you get black. Combine all the colors of light and you get white. 

Ultimately the surface of anything painted would not be as black as a surface covered with something like black fur or hair. That's because reflection of light off a surface helps determine its visibility. For example, a panther is far more invisible in the shade of the jungle than would be a Darth Vader helmet - because the fur of the panther does not reflect any light off its surface. 

So any discussion of the "darkest shade of black" would have to include the patina (surface reflective properties), not just the color of the pigment used in the paint. 

The monolith in 2001: A Space Odyssey was described as being "like a hole in space" more than a color. That is the measure of what the darkest color of black might look like.