"面色萎黄" can be translated into English as "sallow complexion" or "a sallow/yellowish face".
"Sallow" specifically describes a dull, yellowish complexion often associated with poor health or fatigue.
"Complexion" refers to the natural color and texture of the skin, especially on the face.
Both expressions convey the idea of a face that appears dull, yellowish, and lacking in healthy color, which aligns with the Chinese term "面色萎黄".