In Japanese, the words for colors can be divided into two groups.
All colors are nouns in their base form,
but some can be turned into い-adjectives by attaching an い at the end,
and some can not. Below are some sentences containing color words that are い-adjectives.
The yellow cup is dirty.
黄色いカップは汚いです。 kiiroi kappu ha kitanai desu.
The black steam train is slow.
黒い汽車は遅いです。 kuroi kisya ha osoi desu.
(He) has brown eyes.
茶色い目をしている。 tyairoi me wo site iru.
We can place these in front of nouns just as we can with any other い-adjective.
The color words below cannot be turned into い-adjectives however.
We can make them adjectival by using the particle の, just as we can with other nouns.
The green ashtray is heavy.
緑の灰皿は重いです。 midori no haizara ha omoi desu.
(I) bought a gray suit.
灰色のスーツを買った。 haiiro no suutu wo katta.
Pink roses are beautiful.
ピンクのバラは美しい。 pinku no bara ha utukusii. Sentence from Tatoeba