I second the idea of Fudge dye, because it's nicely temporary and will come out within a few washes.

There is always the Manic Panic and Special Effects brands, but they're far more permanent. Unless that's what you want. In which case the easiest way to obtain them is to pop into Wildilocks on Hay St in Perth - next door to Boffins bookshop - and buy yourself a bottle.:)