A hair dye should give you the result you want, but if for example you lighten your hair colour with dye and it comes out too warm, you can use a toner on top of it to neutralise the brassy tones. So to answer your question, you shouldn't and there is no benefit in using a toner before your hair dye. read more
Toner is a blue, grey or violet tinted dye that removes brassy, gold or orange tones in hair. It can be difficult to find in drugstores, but is available for purchase in beauty supply stores, along with developer and everything else you will need. read more