Can I use this on hair that was bleached or colored recently, and what precautions should I take?

Bleaching removes natural melanin and leaves the cuticle highly porous. When an ash shade like 9.0 is applied to such hair, the cool blue-violet pigments can penetrate too deeply and deposit excessively, resulting in a muddy, greenish, or lavender cast that is difficult to correct. If your last bleach or high-lift color service was less than 14 days ago, the cuticle has not fully settled and the risk is highest. A practical approach: wait at least two weeks, treat the hair with a hydrolyzed protein mask twice during that period, then perform the strand test described above. If the strand test shows an overly cool or uneven result, you can pre-pigment ("fill") the hair with a warm gold or copper semi-permanent at level 7–8 for 10 minutes, rinse, dry, and then apply the 9.0. This replaces the missing warm undertones that the ash shade needs to balance against. Always follow the developer volume recommended in the leaflet — typically 6 % (20 vol) for deposit-only on pre-lightened hair — and do not extend processing time beyond the maximum stated.