red ink vs sum of money

red ink and sum of money both are nouns.

Word	Noun	Adjective	Verb	Adverb
red ink	Yes	No	No	No
sum of money	Yes	No	No	No

As nouns, sum of money is a hypernym of red ink; that is, sum of money is a word with a broader meaning than red ink:

Other hypernyms of red ink include amount, amount of money, sum.

red ink (noun)	sum of money (noun)
the amount by which the cost of a business exceeds its revenue	a quantity of money