Goldwell's Soft Color is amazing for tinting back with no damage.

It is a temporary mousse-in colour that does NO damage AT ALL... conditions beautifully and can be reapplied as often as you wish.

If your highlights are particularly light, I and you are darkening more than two levels, I would really make sure to use a warmer tone as using an ash tone when 'tinting back' from lighter to a fair bit darker can garner greenish tones if you aren't careful. When going from platinum back to dark brown, believe it or not, you have to fill the hair with red before using the brown tone-- otherwise you end up green!

Goldwell Soft Color Foam Colorant reviews - Makeupalley

Would love to hear your reviews if you end up using it!