This cloak, heavily dyed with Utterblack, has the power to become fully invisible when the light level is dim enough. Not simply hard to see, but fully invisible, extending several inches out so bare hands and uncovered faces would also be hidden. The slightest touch of light greater than that of candlelight dispels the effect.
The use of Utterblack in its manufacture has the unfortunate side effect of thinning reality nearby its wearer. This could manifest as little more then rather disturbing nightmares, or could even bring the wearer to something malevolent's attention.
A variant of this is the Black Robe of Angius Reft. This full length robe is reversible, with a stylish blue and gold mage's robe exterior, and the Utterblack interior. In addition to its shadow-hiding ability, the robe is resistant to piercing weapons, and has numerous extra dimensional pockets. It is also a Darkness magnet, so its wearer is far more likely to 'randomly' encounter fell beings from beyond the veil, and not in a good way.