You can think of skin that has stopped being its usual colour. Something has happened underneath, and the surface shows it — a knock leaves a heavy blue-grey patch, a shock drains a face until there is no colour left, a feeling too big to hold changes how someone looks in the moment. Livid is the word for that changed surface. It does not fix one shade, which is why it can sit at both ends: the dark of a and the white of a face are the same idea seen from either side.
The supplied source traces livid through Middle English and Old French to Latin līvidus, bluish, from the verb līveō, to be of a bluish colour. The colour meaning is where the word begins, and the other uses are that same changed skin seen in different situations.
來源資料把 livid 一路接回拉丁文 līvidus（帶藍色的），再往前是動詞 līveō（呈現青色）。所以顏色是這個字的起點。其他用法，可以想成都是同一片「變了色的皮膚」，只是出現在不同的情境裡。
Wiktionary entry for livid, supplied in this packet: "From Middle English livid, livide, from Old French livide, from Latin līvidus (“bluish, livid; envious”), from līveō."
Two branches
皮膚的顏色變了
這一組就是核心畫面本身，也是字源直接指向的地方。兩個意思乍看相反，一個暗、一個白，但共同點是「顏色離開了正常的樣子」。
adjective · C1
Used of a mark on skin: dark blue-grey, the colour a deep bruise turns. Marked formal, so it belongs to careful writing — a doctor's note, a report, an older description — rather than to everyday talk.
瘀青似的暗青色
氣到臉上都看得出來
從皮膚移到情緒，但畫面沒有換：氣到臉色變了。可以留意一個線索——來源資料在解釋這個意思時，開頭仍寫著「氣到臉色發白」，等於自己把兩層接了起來。這是概念上的連結，不是在說歷史上一定這樣演變。
adjective · B2
Extremely angry — angry enough that it shows on the person: the face sets hard, the voice goes tight, and they can barely keep it level. Often used when something feels unfair or when someone has been lied to.
氣炸了