"Black is the absence of light, and therefore the absence of colour!" pronounced Gramsci. "Assuming, of course, one is working within an additive paradigm - colour as light. White light is thus the composite of all colours - red, green and blue." The Cow rolled her eyes dramatically. This wasn't helping.
"Of course, if one is working in a subtractive paradigm - colour as pigment, say - then white is the absence of colour and black the composite of all colours - cyan, magenta, and yellow. Technically, it's more of a messy grey, which is usually why printers specify it as the CMYK system, the K being for real black. So yes, black is a pigment, black can be a colour, in that paradigm."
The Cow decided to abandon the attempt. She wasn't about to engage in elaborate discussions about paradigms with people dressed as woodsprites at the door. Instead she arrived colourfully clad in multiple hues.
"Are you colour co-ordinated?" asked the woodsprite. The Cow wasn't sure. "Ah, yes!" cried the woodsprite. "There's pink there" - in her jersey - "and there!" - her fishnet socks. In she went.
It was clear some others had had less reticence in engaging the paradigm debate, but black was by no means universal. An ambulatory marshmallow in radioactive pink glowed from across the hall, and various green ensembles flitted among the blue, white, silver and stone.
The Cow turned to the black-clad teenager sitting next to her. "Is black a colour?" she asked. "Free, free as a free range moth," he quoted back at her, and sunk his teeth into his salome.