Snape's head snapped around, as Professor Sprout raised her wand, and the Potions Master managed to raise a wordless translucent ward between them. But the bolt that shot from Professor Sprout's wand was a dark brown that produced a surge of awful apprehension in Harry's mind; and the brown bolt made Severus's shield wink out before they touched, clipping the Potions Master's right arm even as he dodged. Professor Snape gave a muffled shriek and his hand spasmed, dropping his wand.

The next bolt that came from Sprout's wand was a bright red the color of a Stunning Hex, seeming to grow brighter and move faster even as it left her wand, accompanied by another surge of anxiety; and that blew the Potions Master into the door, dropping him motionless to the ground.

I interpret that as Legilimensed Sprout's magic is Voldemort's magic is Sense of Doom magic. But then how was the troll made immune to sunlight, when Harry touched the troll's skin directly?