"Hello, Hermione."
"Hello, Colin. Need some help with your Potions again?"
Somehow, Hermione had fallen into a pattern of helping Colin with his Potions homework. Just that one subject, none of the others.
"Yeah. Actually, it's an extra credit assignment. Apparently, it's pretty easy to invent a new potion, and since I'm still only at a low A..."
She nodded. "Well, the first thing you'll need to do is look through the Comprehensive List Of All Potions Yet Invented, to make sure your idea hasn't already been done. Scratch that, the first thing you'll need to do is have an idea, the second thing you'll need to do is check the Comprehensive List." Colin frowned, idly nibbling on his thumbnail. "Well, to start with, there are a few broad types of potion..."
"... probably want chameleon skin for the color-changing aspect, right?"
"Yes, and I think some chameleon brain as well, since the potion will be changing intelligently."
"That makes sense. And, of course, we'll need some bits of the people we're comparing."
They had decided - well, Colin had decided, mostly, with Hermione making sure not to steer his project too much - to create a potion that would show how closely related two people are. Somehow, despite all the pure-blood mania and "oh man I am so related to that famous powerful guy" in the wizarding world, this potion had not yet been invented. Hermione suspected that having an easy way to prove a relation would result in many influential pure-blood families discovering things they did not wish to be true.
"All right. Anything we missed?"
"We have a recipe. It's not illegal. It doesn't already exist." Colin gave a sidelong glance to the seven volumes of the Comprehensive List Of All Potions Yet Invented. It had no organizational system. They had had to read all seven volumes. Closely. "None of these ingredients are known to interact in strange ways. I think we're ready to make a test batch."
Seven minutes later, they had two small bottles nearly full of smoky liquid and one large bottle with just a trickle of black sludge.
"And now we put the bits of the test subjects in those two bottles," Colin said, chewing off a bit of his fingernail. "That part is this part, right? Cause last time I did things out of order I had rose-tinted vision for a week."
"Yes, this is that part," Hermione said, carefully removing one strand of her own hair. "It should start giving off a sort of blue mist then." She dropped it in the bottle with the expected result. Colin did the same thing. "Then we pour those two into the final bottle, and since we're unrelated, it should turn..."
Bright orange.
The two of them stared at it for a moment.
"That," Colin said, "is not slate grey."
"No. It isn't."
Bright orange was the color they had assigned for 25 percent relations; cousins or half-siblings. It could be assumed that the relation had been deliberately hidden, therefore, half-siblings seemed more likely.
"Huh. That explains a lot, though."