みどり is not an adjective. It is a noun so you say みどりの... The adjective is 緑色. 緑色なくつ.

Examples of na-adjectives are: しずかです　quiet げんきです energetic しんせつです kind And, yes, when you put it before a noun, it becomes like しずかな　ひと　quiet person げんきな　ひと energetic person しんせつな　ひと kind person

In Japanese, color name is a noun. Only a few of them can become adjectives. あか->あかい、あお->あおい、しろ->しろい、くろ->くろい きいろ（黄色）->きいろい、ちゃいろ（茶色）->ちゃいろい Others can not become adjectives. みどり and みどりいろ are both nouns. You can say 「みどりのくつ」 or 「みどりいろのくつ」, but you can't say 「みどりなくつ」「みどりいろなくつ」. Normally color names can't become Na-adjectives (there might be some exceptions, such as poetic expressions).

"color name + の + noun" is correct Japanese. So みどりのくつ is correct. Example of Na-adjectives is; おおきなくつ (it means big shoes.)

I meant: For Na-adjectives, how is it being used? For example, is it みどりのくつ or みどりなくつ?