Will this shampoo work on my current hair colour — dark blonde, highlighted, or natural grey?

The ash-violet pigments are designed to neutralise yellow undertones, so the visible result depends entirely on how much yellow is present and how light your base is. On level 9–10 blonde, white, or natural grey hair, the effect reads as a clear silver-platinum or cool grey. On medium blonde (level 7–8) the same pigments produce a softer, ashier tone — you will see less brassiness, but not a true platinum finish. On dark blonde or light brown (level 6 and below) the change is minimal because there isn't enough lightness for the cool pigment to show through.

If you have highlights or balayage, only the lightened strands will pick up the tone; the darker base will stay largely unchanged, which can actually create a nice contrast. Very porous or over-processed hair absorbs pigment more aggressively — do a strand test on a hidden section first, and reduce the leave-on time to 1–2 minutes if the tone looks too intense.

This product does not lighten hair. If your goal is to go from yellow-blonde to platinum, you need a lightener/toner service first; this shampoo only maintains or refreshes an already light base.