It happened in potions class. It wasn't really profound, or earthshattering, or anything of the sort; in fact, if Neville hadn't been hopeless at brewing truth serums and Draco hadn't found it amusing to flick a sleeve of paper filled with blind-worm's stings into his cauldron, it wouldn't have happened at all. It didn't change lives, just a few perspectives.

Harry Potter had just been thinking of how much he couldn't wait to finish the class and have lunch; he did not, as a rule, enjoy potions, and added to that, his semi-veritaserum was a very ugly shade of grey, and he knew that even if Snape didn't banish it out of spite, he would likely be getting a zero anyway. He considered the wisdom of asking his Potions professor if he could try again, and finally sourly concluded that he would rather take the zero than suffer more remarks about how his father was an arsehole. He started to try to stabilize his potion with shredded fennel and pixie dust, but before he could even begin to try to fix it, all the liquid in the cauldron abruptly vanished.

"Zero, Potter, see me after class," Snape said, sweeping by him. "Even your father could do better than that!"

Harry shot him an ugly look as he swept away, while Ron fumed from the station next to him and Hermione gave him a sympathetic look. Near by, Neville Longbottom was staring nervously at his cauldron. "It's purple," he said unhappily to Harry, stirring his smoking potion frantically. "What did I do?"

"You didn't bother to read the directions, as usual, Longbottom."

Neville squeaked as the dour Potions Master billowed up behind him. "Did you even think before adding the cayenne? And- pickled squid is not on the ingredients list, Longbottom. How did you even manage to turn a truth serum into Amoris Vinculis? It is obvious that you are incapable of rational thought. No doubt it will shortly-"

The furiously-bubbling potion started to foam up, and then shot straight out of the cauldron, nearly reaching the roof and raining down all over one side of the classroom, as well as the professor.

"-Explode," the teacher finished, as the eggplant purple liquid splattered most of the students on the Gryffindor side. "I admit that I am surprised that you did make a viable potion."

"Amoris Vinculas, sir?" said Hermione, surprised. "Isn't that-" she blushed frantically, "a 'purity potion'?"

"Of a sort." Professor Snape looked as if he had been forcefed a lemon- or something worse. "Although does not show virginal status, but rather relationship status."

"But what does it do, sir?" Draco Malfoy broke in.

Snape was silent for a long time. "It causes, well, a visible aura," he said, "As demonstrated by those who have been splashed with the substance. Pink is for passing fancies, a crush, if you will. Green is for a relationship. White is for having no interest in romance, and yellow is for lust. A marriage bond shows gold. And blue, blue is for unrequited love. The stronger the hue, typically the stronger the emotion."

Sure enough, those who had been splashed with the potion, mostly Gryffindors, but with a few Slytherins, were beginning to glow as the potion seeped through their clothes, and Harry, curious despite himself, glanced around at those affected. Most glowed various shades of rosy pinks. Daphne Greengrass, the "Ice Queen of Slytherin", glowed white, to no one's surprise. Ron and Hermione glowed a matching spring green, so that several of the Slytherins started cat-calling. Seamus Finnegan had an ugly bright yellow shine that wavered in and out, and Pansy Parkinson glowed a dismal grayish periwinkle. Harry looked down at himself, feeling awkward that his love life, too, was on display, and blushed to see the pink shimmer that he knew had to do with Cho Chang.

And then he looked up. And his breath caught in his throat. Hanging around Professor Snape, dark as his robes, was a curtain of lapis lazuli blue. Unrequited love.

"Professor-?" Pansy Parkinson began.

Snape cut her off. "It lasts an hour. Class dismissed." And without a word, he stalked out the back entrance of the classroom. Harry was one of the few who noticed that the Dungeon Bat's shoulders were shaking ever so slightly.