Devil's Sight (PHB p119) allows someone to "see normally in darkness":

Devil's Sight
You can see normally in darkness, both magical and nonmagical to a distance of 120 feet.

Our ideas of normal vision includes lightness differences: uneven surfaces like crumpled paper catch the light differently, and even a tree in a dark new moon night may cast a subtle shadow away from the moon.

Would someone with darkvision or Devil's Sight be able to discern those lighting differences, or subtle shadows (if there's a faint light source to produce them), that we consider vital for "normal" vision? Do the rules have anything to say, or is there guidance from closely connected material or other editions available?

This is a "magical" ability for the most part, but it seems like if you don't need light to see normally, you may not be able to discern different lightness levels at all.