I haven't timed my hair colouring for Christmas very well. I had roots (light brown) and highlights (blonde) done 4 weeks ago. I now 1/2 " of horrible silvery /white re growth at my roots. I can't get an appointment before Christmas so- I was wondering - would it be ok to buy a home hair dye and just touch up my roots myself, or will this muck up my usual root touch up in the new year?