Maybe someone else knows of a way to do this, but from my limited experience, trying to lighten hair almost always comes with a consequence, worse depending on how much color you want lifted. Tends to damage the hair cuticle and make the hair more porous and dry. That said:

Some use lemon juice or honey (over time), for a subtle lift in color. Color Oops is used by some. The claim is that it's gentle, but I don't know too much about it. It does include citric acid, which could be harsh, but it's one of the last ingredients so I'm not sure.
3b/c?

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