Clothing is a Motif because it can represent the characters traits and characteristics
"Her mother, in contriving the child's garb, had allowed the gorgeous tendencies of her imagination their full play; arraying her in a crimson velvet tunic, of a peculiar cut, abundantly embroidered with fantasies and flourishes of gold-thread."
Darkness represents Dimmesdale's hidden sin which has not been confessed or revealed yet. "No eye could see him, save that ever-wakeful one which had seen him in his closet, wielding the bloody scourge."
Daylight represents Hester's sin but instead of it being hidden, it is open and revealed so that everybody knows.
"The scene was not without a mixture of awe, such as must always invest the spectacle of guilt and shame in a fellow creature"