darkness vs skin colour

darkness and skin colour both are nouns.

Word	Noun	Adjective	Verb	Adverb
darkness	Yes	No	No	No
skin colour	Yes	No	No	No

As nouns, skin colour is a hypernym of darkness; that is, skin colour is a word with a broader meaning than darkness:

Other hypernyms of darkness include complexion, skin color.

darkness (noun)	skin colour (noun)
a swarthy complexion	the coloring of a person's face
having a dark or somber color
an unenlightened state
an unilluminated area
absence of light or illumination
absence of moral or spiritual values