White Roots & Natural Hair Color

A: I completely understand your frustration. Over-bleached hair can be really distressing, especially when it's so much lighter than what you were aiming for. The good news is that you can definitely work toward getting your natural color back, though it will require some patience and the right approach.
Here's what I recommend for getting back to your natural darker blonde shade. First, you'll want to choose a hair color that's approximately one to two shades lighter than your natural color, not exactly matching it. This might seem counterintuitive, but over-bleached hair tends to absorb color much more readily than virgin hair, so starting a bit lighter will help prevent you from going too dark on the first application.
For the mixing process, you'll want to use a 10-volume peroxide developer rather than the standard 20-volume that usually comes with box dyes. The 10-volume is much gentler and will deposit color without causing additional damage to your already compromised hair. You can find 10-volume developer at most beauty supply stores or online.
When you're ready to mix, combine one ounce of the 10-volume developer with one ounce of a good quality deep conditioner. Then add this mixture to your hair color, which typically comes in 2-ounce tubes or bottles. The conditioner serves multiple purposes here . It dilutes the color slightly for a more gradual result, adds moisture back into your damaged hair, and helps the mixture spread more evenly.
Before applying the mixture all over, I strongly suggest doing a strand test on a hidden section of hair first. This will give you a preview of how the color will turn out and help you avoid any unwanted surprises. Choose a small section underneath your hair near the nape of your neck, apply the mixture, and let it process for the full time to see the results.
When you're ready for the full application, work systematically through your hair, making sure to saturate all the over-bleached areas thoroughly. Pay special attention to those white roots on top, as they'll need the most coverage. Allow the mixture to process for about 20 minutes, checking the color development every 5 minutes or so after the 15-minute mark.
Keep in mind that getting your hair back to its natural state after significant over-bleaching often takes multiple sessions. It's a gradual process, and rushing it by using stronger developers or darker colors can result in muddy, uneven coloring or even more damage to your hair.
While you can attempt this at home, I do want to emphasize that consulting with a professional colorist would be your safest bet, especially given the extent of the lightening you've described. A professional can assess the current condition of your hair, determine the best approach for your specific situation, and potentially save you from further mishaps.
If you do decide to proceed at home, do so at your own risk and remember to always perform that strand test first.
©Hairfinder.com
See also:
Hair coloring
What does the developer do?