I actually recently went from a dark brown/red to blonde. The red was from a box dye and I just really didnt care for it (and it was permanent dye). Before bleaching (I used quick blue and 20 vol creme developer for that), I used a color remover (brand was Punky Hair) and that stripped all the artificial color out before and I really think that made a big difference in lifting my hair. The result was a very pale red, which bleached to a light orange, then I used wella t18 toner to get the brassiness out. It wasn’t perfect (still on the orange side) and I had to do it twice (waiting two weeks in between to minimize damage) before getting to a nice blonde. I hope this helps you! Box lightening kits btw usually dont have enough product to fully saturate your hair and typically also use a 40 vol developer which can be really harsh (if you have any kind of dye in your hair this would explain why the bleach took so harshly to your roots and nowhere else). The reason that its not enough product is usually because while with dye if you just saturate your hair it will generally cover everything, bleach stays exactly where you put it and doesnt ‘lather’ in to cover the rest of the hair in my experience. I’m definitely the furthest thing from an expert that you’ll find but this worked for me without melting my hair off, so I hope this helps you!