Tram, you're asking a very complex question. This is the sort of thing an English speaker knows how to construct but doesn't have a ready explanation for.
These sorts of questions may be better asked on a site devoted exclusively to English grammar, like english.stackexchange.com (their top upvoted questions are often quite fascinating, especially for an English speaker).
The construction you quote seems, from their answer, to be an actual English grammar rule unto itself: by taking a noun that an object possesses (leg, ear, surface, head, whatever) and adding ed to the end, one can prefix the word with a quality to form a new adjective:
- a six-headed, seven-mouthed, purple-skinned elephant.
- a burgundy-surfaced, six-legged, seven-drawered desk (this last adjective, seven-drawered, sounds excessive and tinny to my ear).
I found a couple answers on the mentioned website to answer this. This question and answer https://english.stackexchange.com/questions/2212/do-adjectives-ending-in-ed-derive-from-words-that-were-once-used-as-verbs/2254#2254
seems to deal semi-tangentially with it. This one seems more direct and discursive: https://english.stackexchange.com/questions/148061/compound-adjectives-and-ed
If you note from some of their answers, this phenomenon is not only limited to -ed but also includes many past-tense seeming forms (well-lit). These alternatives to -ed may stem from actual irregular verbs made into past-tense whereas the rest of the words are pseudo-verbed nouns for the purpose of the adjective.
I hope that helps.