You can tint white chocolate various colours if you use oil based colours. Water based colours will cause the candy melts to "seize up". I have been told that powdered colours also work, but I've never tried them. I have found oil based colours online and in craft stores (and Bulk Barn). Paste food colour can be used, but I find that they tend not to colour the chocolate evenly and you get lots of specks of colour in the chocolate because of the water in the gel or the paste.