We Have Fuligin

Fans of Gene Wolfe's magnificent Book of the New Sun far-future novels will recall that the traditional color of the Guild of Torturers was fuligin - a fictional light-absorbing hue blacker than black.

It now exists.

I think that almost makes up for the now shaky scientific basis of Wolfe's technology for transferring memories from person to person.

If you want fuligin cloaks or garments in a D&D game, you will have to visit one of the Underdark's disreputable bazaars, bringing with you at least 1000 gold pieces worth of treasure; or take them from those few underground elves who have learned to weave elemental darkness into spider silk. Covering your body near-completely with fuligin, with black masks or veils over one's face, black gloves, and all equipment painted black, gives a +4 on d20/+20%/+1 on d6 for hiding in shadows. Wearing fuligin in public will attract awe, fear and no small amount of attention.