No, that's wrong.
Hikaru and Kaoru Hitachiin are pulling a prank! They've bought a LOT of Shampoo bottles around the town and put green dye in them. They brought them back to the store, complaining about them. If you want your character to have green hair, just go ahead and complain about it on good ol' Saint Patty's day!
YOU TOO CAN LOOK THIS SEXY.
Also, Miroku will probably be running around pinching girls, even if they're not wearing green.