فَإِذَا هُمْ مُظْلِمُونَ
Then suddenly they are in darkness.
This ending gives prominence to the darkness perceived after the departure of daylight. The abrupt construction conveys the sudden awareness of the resulting condition, strengthening the metaphorical scene.
The removal of daylight and the arrival of darkness are linked by sequence and succession. The metaphor cannot be accounted for solely by comparing the visual color or shape of skin with daylight.