Does that mean 'unpardonable curses'? Cruciatus, Imperius, and Avada Kedavra used to be called 'The Unforgiveables' here, but now they're 'the Cardinal curses.'

I don't think it happens OFTEN but it is allowed, for professors and the Head Boy and Head Girl are also allowed to do it (you know, I don't know if they'd be allowed to do it on you lot or not, though. Probably not! I imagine the teachers would be allowed to though.)

Regarding the pink parchment -- Cassandra was leaving notes for Professor Sinistra on pink parchment, and they had a curse cast on them that could have hurt her. So the problem wasn't the colour, definitely. (A lot of girls in Slytherin have some pink parchment -- Hydra gave it out as a present one year, since she loves pink parchment and thought everyone ought to have some. So Cassie's Cassandra's might have come from Hydra, but no one blames her, certainly.)