Lightening Dark Hair with Lemon Juice?

I have dark brown, shoulder length, thick hair and I want to dye my hair purple and blue with Kool-aid. I need to lighten it first. My mom said I can only lighten it with lemons/lemon juice. How long do I need to sit in the sun with it and all that? Do I need to wash it out afterwards? I need help.

By Jazmine