noun
Refers to a person's emotional state or feeling, often as perceived by others. Somewhat literary or formal; in casual speech 気分 or 機嫌 are more common.
彼の気色をうかがうような態度が気になった。
I was bothered by his attitude, as if he were gauging my mood.
noun
Describes the expression or look on someone's face, especially as an outward sign of inner feelings. Often used in set phrases like 気色が悪い (looking unwell or creepy).
彼女は気色が悪そうな顔で部屋を出ていった。
She left the room with a sickly expression on her face.
あの絵はなんとなく気色が悪い。
That painting is somehow creepy-looking.
表情 is the standard word for facial expression. 気色 emphasizes the mood or health reflected in the face, and is often used in negative phrases like 気色が悪い.
Compound of 気 (spirit, mood) and 色 (color, appearance). The exact historical derivation is uncertain, but the word has been used since classical Japanese to mean both inner mood and outward expression.