Noting the difference in how sunlight affects the reds vs. the black, I think that in both cases it's an elemental effect/attack against each species, but the severity of the attack (and it's effective Weapon rating) would be higher against a black court than it would against a red court. Have a look at fire in the books (not quite sure where, don't have mine with me at the moment) and how you'd deal with it if your character were in a burning room or building, then adapt it to sunlight.
Both Bianca (book 1) and Kelly Hamilton (book 3) were hit by sunlight, you can extrapolate how deadly it is to the Reds from that.
I can't think of any time where Mavra or any of her various brood are ever exposed to sunlight, though, so I don't have any concrete examples.