When you use more than one adjective to designate a single color (like "light blue," "dark green," etc.), neither of the adjectives changes according to the noun it modifies. For example:
"Il a les yeux bleu clair et les cheveux brun foncé."
"He has light blue eyes and dark brown hair."
While awkward sentences still creep in to Duolingo's exercises, it is not forcing anyone to use unnecessary words. The "des" in "des bottes" is used because it is the only way to express the idea of plural boots in French. In this sense, "des" is the plural of "un/une". There is no counterpart for this in English although some people have the mistaken idea that "des" must be translated as "some".
"Des" is used (here) as the plural of "une". There is no counterpart in English. Some people have the idea that it must be translated as "some". That is not true. It is not absolute wrong but this sense of "some" is almost always ignored in English whereas "des" is absolutely required in French. So to reinforce Ripcurlgirl, avoid adding unnecessary words. Be aware that "some" has other meanings that get conflated with this one also. Consider "certain" or "quelque" as examples.