Chamomile, vinegar, lemon, honey... I tried them all and they all worked on me. Don't expect big, fast changes. It takes time.
My favorite one is chamomile 'cause it's gentle on the hair and it doesn't make it dirty. Take 2-3 cups of hot water (boiling), steep 4-5 chamomile bags in it for about 20 minutes. Let the water cool down, then pour it on your scalp. Let your hair dry (best if it's in the sun).
Haha No natural method will help you change your hair color so drastically. I say during the Summer be out in the sun a lot - with lemon juice on your hair - it will lighten it, but NEVER by that much + that second color is a lot more golden than the first - that's a whole different thing - only either natural like that or with dye.
John Frieda makes lightening shampoos for blondes. There is a highlight enhancer as well as a lightener. I've used both. They do the truck but they can be drying, so I would mix it up with a deep conditioner every few days.
I use sun in, although you have to spread it out carefully, otherwise you could have a spot that's blonder than everything else. It works well for me though. I just use it for the bottom half of my hair to make it kind of like an ombré. That way when my hair grows out in the winter it doesn't look weird.
Well I've bleached mine before and all though people say it dries out ur hair, if u deep condition once or twice a week it'll be fine. Other wise try puttin lemon juice in your hair and sitting out in the sun, that can sometimes make it lighter