I think that bleaching here, involves bleaching the whole hair with the white color , so then when it is dyed, the color becomes more stable & natural looking:as we say in Egyptيشتغل على ماية بيضا "بالعامية طبعاً"
Pls see this search, it has images of bleached hair, you'll see that color of original hair is whitened as a prior step to dying it. Also if you turned within the same search to "Web Page", you'll see info. & facts about hair bleach...Thank you
http://images.google.com.eg/images?hl=en&q=bleaching the hai...
The translation workplace 
