Here are some awesome colours for dip dyeing your hair:
Demi Lovato in pink dip dye
Jessie J did hers in dark purple
Yellowish orange; Not so popular but still a nice colour nonetheless.
Also, there are temporary dip dyes but it will wash out once you wash your hair, so that's quite wasting XD
However, if I were to try, I want a three tone dip dye with three of my favourite pastel colours;blue, purple and pink =)