When they are nouns, colour words are typically used in the singular with no determiner.
The 60-year-old actress, dressed in black, told of her sorrow as she was mobbed by photographers.
I like blue.
Her nylons were just the right shade of brown.
Cristina always wore red.
Yellow is my favourite colour.
However, the more frequent colour words can be used in the plural, or in the singular with a determiner and a modifier or qualifier, to refer to different shades of a colour.
In autumn, the changing colour of the beech forests drapes the country in browns and reds.
It is light and airy, painted in a green which Candida mixed herself to match the green of the leaves and trees outside.
Its hull is a deep red and its upper decks white.