swarthiness vs complexion

swarthiness and complexion both are nouns.

Word	Noun	Adjective	Verb	Adverb
swarthiness	Yes	No	No	No
complexion	Yes	No	Yes	No

As nouns, complexion is a hypernym of swarthiness; that is, complexion is a word with a broader meaning than swarthiness:

Other hypernyms of swarthiness include skin color, skin colour.

swarthiness (noun)	complexion (noun)
a swarthy complexion	the coloring of a person's face
	(obsolete) a combination of elements (of dryness and warmth or of the four humors) that was once believed to determine a person's health and temperament
	texture and appearance of the skin of the face
	a point of view or general attitude or inclination
	a combination that results from coupling or interlinking

swarthiness (verb)	complexion (verb)
	give a certain color to