"The cat has a red boot."
Translation:Le chat a une botte rouge.
Rouge is used to modify both masculine and feminine nouns.
Rouges is the plural form. Since the sentence mentions one boot, the correct translation is 'une botte rouge.' Hope this helps!
Botte rouge: Red boot
Rouge botte: incorrect; adjectives of colour always come after the object they modify
in French, most adjectives come after the noun. Major exceptions like "beau", "jeune", "bon" and "petit" are often taught as the "BAGS" adjectives Beauty, Age, Goodness, Size. Words like this go before the noun they describe. Example: "Un chat noir" (a black cat) BUT "Un petit chat" (a small cat)