I have done this to my hair on numerous occasions. I have managed to go opletely blonde within a matter of 4-6 weeks without killing my hair!!:) What has worked for me was to use a color remover several times and using (I know this may sound crazy) Metalex from Sally beauty supply. You can do this several times as well with 30 volume and heat for 15-30 min. It will condition the hair and help get out the majority of the color. Store bought or not.You should be able to get them to a nice light brown with a few highlights, increasing a few more foils every visit. I would never reccommend they go strictly to blonde from the start. Instead your consultation should let them know you can get them there over the course of a few months while saving the integrity of the hair. With the right products and our guidence anything is possilbe:)
P.S.....They have to be willing to leave the salon with all the products you reccommend and be dilligent about using them or DO NOT perform the service!!!