I have always just used color adjectives by themselves, but I am wondering when/if one can use them with the word "couleur". For example, can one say the 2nd and 3rd variants of the first sentence below? Il porte une chemise rouge. Il porte une chemise couleur rouge. Il porte une chemise de couleur rouge. And would the answer change if the color involved were also a noun, such as "or"? Lastly, if the color were an adjective with a distinct feminine form, such as "vert", would it agree with "couleur" instead of the noun whose color is being discussed. Merci d'avance.