Colouring your hair at home can lead to a multitude of disasters: if the colour is lighter than your existing colour you will end up with root glow (this is when your roots are brighter/lighter than the mid lengths leaving you with an uneven result, if the colour is too dark then the colour could sink or grab existing pre-lightened hair resulting in darker areas where the porosity of the hair shaft differs. ...More >
My suggestion would be to ask your salon for a colour which has more longevity to it, such as ombre or dip dye as this leave behind minimal roots and fewer trips to the salon. Alternatively you could enquire at your salon about their training days and be a model for that as you would be charged a much smaller fee.
If you do decide to go ahead with home colour, remember to skin test with the products 48 hours before applying.