Yes, ink is a singular, common, concrete noun, a word for a thing.
The word ink is also a verb (ink, inks, inking, inked), writing with ink or applying ink; used informally for to sign a contract.
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There is no standard collective noun for the noun 'ink'.A collective noun is an informal part of speech, any noun that suits the situation can function as a collective noun.In the past, you would have looked for a bottle of ink, but today you are most likely looking for a cartridge of ink.
It's just "ink," as in "My pen uses a lot of ink."
Proper
The possessive form of the plural noun pens is pens'.Example: All of these pens' ink is blue, none are black.
The word colors is a noun, a plural form for the noun color. The names of colors are also nouns, for example red, blue, yellow, etc. The names of colors are also used as adjective, words to describe a noun. Some nouns that use colors are paint, enamel, fabric, chalk, ink, dye, makeup, etc. Most physical things have a color.