Can Aphotic Wisps be cast on a black creature that has fear?
You can target any* creature, it doesn't matter if the creature is black and/or has fear. This is because all the card says is "Target creature", not something like "Target non-black creature without fear". Dross Prowler is a creature thus it is a valid target for "Target creature".


  114.1a An instant or sorcery spell is targeted if its spell ability identifies something it will affect by using the phrase “target [something],” where the “something” is a phrase that describes an object, player, or zone.


*barring things like hexproof, shroud and protection