I've been having a full head of highlights for as long as I can remember. Times and finances have been hard lately so I stupidly thought a full box colour carefully matched to my blonde would be fine and not break the bank.
This was my first time so followed it really carefully. I did a strand test, left it on my roots longer etc. the colour on my lengths is amazing and I love it. But my roots are ginger!!!
This mistake is not as rare as you would think and I certainly have had to fix a few of these myself. The reason it went ginger on your roots, is that the mixture is not strong enough to lighten your hair and deposit the tone to make it blonde. Highlights often have a mixture of colours incorporated into them, using a bleach product to get that pale creamy colour which is stronger than the dye you used.
Home hair colours are a little one shade fits all which makes it difficult to judge which one is best, also the girls on the box with the beautiful hair more than likely haven't used it.
Now what can be done? Believe it or not you need to have your roots very slightly darkened as highlights never quite get to the root and what you are seeing now may look too bright and monotone.
Then you need to have the root area re-highlighted to break up the darker root area, this then should have balanced the colour out and you can continue with having highlights.
John Clark at Brooks+Brooks, London