black
黒 centers on the color black and things that are dark or blackened.
黒 is a pictograph of a person with a tattooed or blackened face, later stylized into the modern form with 田, 土, and 灬.
The top 田 looks like a soot-covered window, the middle 土 is dark earth, and the bottom 灬 is a fire's ashes. Together they make black.
For コク, imagine a black cock (rooster) covered in soot: cock -> コク, and its feathers are pitch black.
black
black
black person
darkness
Meguro City (special ward of Tokyo)
black and white; monochrome
black curtain
pitch black
unbarked lumber
(being in) the black; surplus
blackboard
black (colour, color)
jet-black; pitch-dark; raven-black; stygian
black spot; black dot; bull's-eye
Kuroshio Current; Japan Current
Black Sea
dark; blackish
black and white; right and wrong
central pillar (of a building)
black clothes
graphite
dark (skin, complexion, etc.); swarthy; tanned
thick fog (of suspicion); black veil of secrecy; covered-up crime, unethical act, etc.
black smoke