Snape cringed inwardly at Marlene's idea of 'appropriate to celebrate'. Part of his mind was already riffling through a very long list of undetectable potions, even as he gathered all his courage and looked down at himself.
He breathed again at the sight of Slytherin-green and silver. That could have been so very much worse. Unicorns and rainbows worse! Out of sheer relief he actually gave Marlene a pat on the shoulder. It was the sort of cautious pat bestowed on a wild animal or potential explosive.