I posted a while back trying to make the transition from red to blonde. Your advice was really great, after a couple of bleach baths, colour b4 and some hi-lights, it was looking quite nice, but I felt I didn't get close enough when hi-lighting to my roots, so just always felt my roots were dark.
My next step, I bought Superdrug permanent ash blonde, and did an all over colour, which I was quite pleased with, it still has some warmth here and there but overall not too bad. I use superdrugs ash toner, and silverising shampoo too. Now i'm due to do my roots, I was wondering if I can add any bleach or developer to the shop bought pack? Just for a tiny bit of extra oomph?! I feel that the last time my roots were just a little bit brassy. I have 20, 30 and 40 vol developer and also some powder bleach, (was really impressed with the superdrug colour btw, and it was only about £3!).