I PROMISE you can do this and it will help your highlight last longer and your roots be less noticable if you do it right.
First, buy the cheapest box of hair color out there (I happen to have a Revlon one under my sink and it retails for about $2.66 at Walgreens).
Second, you are NOT going to leave this product on your hair for more than a TOTAL of 10 minutes. Starting like this: ONLY use the color "light ash blonde" (TRUST ME – it won’t be blonde, blonde when we apply it the way we are going to).
Follow the directions on the box to a TEE as to how to mix the product. At the roots of your hair and near your scalp apply the color (saving some for your ends).
Set your timer for 5 minutes.
At the 5 minute mark, apply the rest of the color through your hair and leave it on for 2 more minutes.
The key to remember is the longer you leave it in, the lighter the color will become, so only leaving it on 7-10 minutes MAX is crucial.
Last, rinse thoroughly (don’t use shampoo, just rinse for 5 solid minutes – I rinse it in the shower) and be sure to use the conditioner they provide.
Waahh-laa!
You’ve just extended the life of your color at least another 6 weeks and save a TON of $$$ (not to mention time spent at the hair salon!!!).

What color hair did you start with? Have you seen this work for other hair colors? Are these directions for a root touch up? I’m interested, but quite confused.
I have dark brown hair and I highlight it blonde (to keep up with the grey ~sigh~). I’ve not seen it used on other colors.
The directions would be for a touchup – it just buys you time inbetween appointments.