No, no, no, Hirayuu is absolutely wrong. い is used often as an addition to color when it is used as an adjective 赤→赤い。緑 is already a の adjective. 緑の車 "green car".
In cases like オランジ, which is orange, the fruit (and you can use this with other fruits too, or anything with a distinct color, salmon for instance) you can use iro to specify the color オランジ色 "orange-colored". It is less common with other colors, as the colors themselves already are more often than not の or な adjectives.
I agree that sometimes there is more than one way to define a word, but in this case it would never be correct to define やさい as "green" with no s. "Green" is a color. やさい is something you eat.