كتشبيه غرة الفرس بالصبح وعكسه
As in likening the white marking on a horse's forehead to dawn, or the reverse.
Ghurrat al-faras refers to a conspicuous light or white marking on a horse's forehead. When the marking is compared with dawn, dawn functions as the familiar source of brightness. When dawn is compared with the marking, attention may shift to the special shape and prominence of a bright patch.
Both arrangements have an intelligible respect of resemblance, but their emphasis and purpose can differ. Reversal may become a full rhetorical reversed simile when the context asserts superior excellence; a mere exchange of grammatical positions does not automatically achieve that effect.