In the phrase "color spectrum", what part of speech is color? What formal or functional evidence supports your identification?

Question

The sentence in its entirety is: "The way people talk about the color spectrum, and even perceive it, varies from one speech community to another, although all humans eyes see the same colors because colors have their own reality in the physical world."

My vague answer: Color is a noun describing the word spectrum acting as an adjective. The formal and functional features I've been able to come up with is the word's appearance, the position in the sentence, and it's occurrence before the word spectrum denoting that it is modifying or describing that word.

How would you answer this question?

Further context: This is a question in a book I'm studying, analyzing English grammar. The section is form-class words and the goal is to give supporting criteria of form (morphology) and function (sentence position) to justify the assignment of a word to a given form class. The book gives rule of thumb tests for the four parts of speech that tests its formal and functional properties if that makes sense.

For example, a test for the parts of speech is if the fit certain frame sentences, this is to test the position. Adverbs are more likely to be at the end, adjectives are tested for their ability to follow intensifiers, like very.

Answer 1

I would say that it is better analyzed as a noun than as an adjective. I don't know, but it seems possible to me that it is a compound word, and I'm not sure it even makes sense to assign a part of speech to a component of a compound word, except for in the sense of "is derived from that part of speech" (e.g. should we say that the "black" in "blackbird" is an adjective? or just that is is derived from an adjective?).

"Color" has no obvious adjectival morphology

The word "color" has no particular formal features that mark it as an adjective (for example, it cannot be divided into a stem and an adjectival suffix like -y, -ive, -al).

It makes sense that "color" has no morphological features characteristic to adjectives, because it is derived etymologically from a Latin and French noun, and is used as a noun in present-day English.

The stress pattern of "color spectrum" is consistent with a noun-noun compound analysis

The word seems to behave like a compound word in that for me, the primary stress can only go on the first syllable of "color" (aside from in highly contrived circumstances, like abnormal stress to emphasize the "spectrum" part). In an adjective-noun sequence, I believe it's usually possible to put the primary stress on the noun. That said, the evidence of stress doesn't seem to rule out "color" being an adjective because it seems like some adjective-noun sequences typically have primary stress on the adjective (see the following Linguistics SE question: Stress rules in English adjective-noun combinations).

The word "color" is certainly used as a noun in other contexts, but is not typically used as an adjective in other contexts

As you mention, adjectives often can be used after the intensifier "very" (e.g. "very good") but "*very color" doesn't seem to be valid. (This test doesn't prove that "color" isn't an adjective, because some adjectives cannot be modified by "very" in some contexts: e.g. "*the very electromagnetic spectrum" sounds bad even though "electromagnetic" has adjectival morphology (the suffix -ic) and is presumably an adjective.)

"Color" also doesn't seem to be used as an adjective in predicative position.

To summarize, as far as I can tell, there is little external evidence supporting an analysis of "color" as an adjective.

Another language, German, has noun-noun compounds that express the same meaning

While there is no guarantee that an English construction will parallel the grammar of a synonymous construction/word in another language, I think evidence from other languages can provide some information about what structures are possible.

When I look up "color spectrum" using Linguee, it turns up a number of German translations that appear to be unambiguous noun-noun compounds, not adjective-verb sequences, such as Farbspektrum, Farbenspektrum, Farbskala, Farbpalette. This indicates that in a language that is somewhat closely related to English, a noun-noun compound can be used to express this meaning.

It is easier to analyze the structure of the German examples because noun-noun compounds are consistently written together without spaces in German, unlike in English.

Answer 2

In a more "traditional" grammar treatment, I'd call this a noun adjunct. But a quick Google search of "form-class words" points at a rather unorthodox approach to grammar

One of the reasons that grammar is approached in various ways is because grammar is an abstraction. The real English isn't as precise as grammar rules suggest. And this example shows a nice border case.

Is "color" a modifier of "spectrum"? Consider the meaning of "spectrum". It is the collection of all colors (Literally). Now, if we consider another collection, say a "stamp collection", it's clear that both words are nouns. We could also say "a collection of stamps" to make that clear. So, one can argue that "color" is indeed used as a noun here.

That said, I can see how you'd call it an adjective. In "color theory", it's already appearing more as an adjective, and in "color television" even more so.