Pale Green, by
flambeau(HP, Harry/Snape)
Torch, being terribly perverse, took what seemed to be an implausibly unwriteable scenario originally presented as a challeng (Harry tells Snape he's a sexy bitch, and he wants him to take him to his secret love nest and show him his magic wand) and turned it into a sexy, disturbing little story. Then gave it to me for my birthday! So, I'm biased, but I think you'll like it.
Harry bit his lip. He tried to keep perfectly still as Snape's fingers moved across his shoulder, but when the first fingertip touched his bare neck, he shuddered. "I really think I should go now," he said, and his voice was quiet and sort of shaky.
"Perhaps you should." Snape's voice sounded different, too, and his dark eyes didn't fully meet Harry's. The fire crackled. Harry wasn't sure he could feel the rest of his body, just that small, bare part of his throat where Snape's fingertip moved in short, soft strokes. "If you think you've learned your lesson."