inkiness vs coal black

inkiness and coal black both are nouns.

Word	Noun	Adjective	Verb	Adverb
inkiness	Yes	No	No	No
coal black	Yes	No	No	No

As nouns, coal black is a hyponym of inkiness; that is, coal black is a word with a more specific, narrower meaning than inkiness:

inkiness: the quality or state of the achromatic color of least lightness (bearing the least resemblance to white)
coal black: a very dark black

Other hyponyms of inkiness include ebony, jet black, pitch black, sable, soot black.

inkiness (noun)	coal black (noun)
the quality or state of the achromatic color of least lightness (bearing the least resemblance to white)	a very dark black