blue-black
黤 centers on a dark, muted blue-black color, like a deep shadowy indigo or the color of a bruise.
黤 combines 黑 (black) with 奄, which likely contributes the sound. The character expresses a dark, blackish-blue color.
The left side 黑 means black, and the right side 奄 looks like a person under a roof. Imagine a person standing in a dark room, their skin looking blue-black in the dim light.
For エン, picture an inkwell of blue-black ink: the 'en' in inkwell cues エン, and the ink is the deep blue-black color of 黤.