"面色萎黄" can be translated into English as "sallow complexion" or "a sallow face".
"Sallow" refers to a yellowish or pale complexion, often due to poor health or fatigue, which captures the essence of "萎黄" (wěi huáng, meaning withered and yellowish).
"Complexion" emphasizes the overall appearance and color of the skin on the face.
Alternatively, you could also describe it as "a yellowish and lackluster complexion" for a more literal and detailed translation.