ink vs red-ink

ink is a noun but red-ink is not a noun.

Word	Noun	Adjective	Verb	Adverb
ink	Yes	No	Yes	No
red-ink	No	No	Yes	No

As verbs, red-ink is a hyponym of ink; that is, red-ink is a word with a more specific, narrower meaning than ink:

ink (noun)	red-ink (noun)
dark protective fluid ejected into the water by cuttlefish and other cephalopods
a liquid used for printing or writing or drawing

ink (verb)	red-ink (verb)
fill with ink	mark with red ink
mark, coat, cover, or stain with ink
append one's signature to