"The colors of the costume are black and blue."
Translation:Culorile costumului sunt negru și albastru.
If colors is plural, I would have expected "negru și albastru" to instead read, "negri și albaștri." Shouldn't these adjectives agree in number with the noun they are modifying?
Here "negru" and "albastru" are used as nouns, not as adjectives, so they do not have to agree in gender, number and case with the noun "culorile".
Also don't forget that "culoare" is a feminine noun, therefore the adjectives should have read "negre şi albastre" if they had agreed with the noun (which is not the case here).