Wella used to do a 'on-off' hair dye system. The idea was that you could strip the dye off your hair if you didn't like it. Not sure if it's still going but you might find it in places like SemiChem/Savers etc. They tend to have older stock. The stuff is a gel, it does smell quite horrible but if you wash your hair afterwards you shouldn't be able to smell it. It won't strip everything out your hair, but it should significantly lessen the amount of time that it shows up for.