rosiness vs skin colour

rosiness and skin colour both are nouns.

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

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

Other hypernyms of rosiness include complexion, skin color.

rosiness (noun)	skin colour (noun)
a healthy reddish complexion	the coloring of a person's face
a dusty pink color
a rosy color (especially in the cheeks) taken as a sign of good health