يَوْمَ تَبْيَضُّ وُجُوهٌ وَتَسْوَدُّ وُجُوهٌ ۚ فَأَمَّا ٱلَّذِينَ ٱسْوَدَّتْ وُجُوهُهُمْ أَكَفَرْتُم بَعْدَ إِيمَـٰنِكُمْ فَذُوقُوا۟ ٱلْعَذَابَ بِمَا كُنتُمْ تَكْفُرُونَ
Yawma tabyaddu wujoohunw wa taswaddu wujooh; faammal lazeenas waddat wujoohum akafartum ba'da eemaanikum fazooqul 'azaaba bimaa kuntum takfuroon
On the day when some faces will be bright and some faces will be dark — as for those whose faces are darkened: did you deny after your belief? Then taste the punishment for the denial you held to.
Arabic already used a whitened face for vindication and a blackened one for disgrace, the idiom behind the man in Surah An-Nahl whose face darkens at news of a daughter, so the image carries public standing before it carries colour. Whether that day makes the idiom literal or keeps it figurative is a question the commentaries leave open. The verse also lands directly after the warning against splitting into factions.