What Is Double Process?
Literally Everything You Could Ever Want to Know About Double Process Hair Dye
23
Jeanise suggested using Milbon Replenishing Shampoo and Conditioner (sold at salons), to extend colour. The one time I washed my hair since the double process, I used a OGX Lavender Luminescent Platinum Shampoo. I haven't noticed much colour fade, so I'm pretty happy with the results of that drugstore option.
Since I heat-style my hair more often than I care to admit, I use Briogeo Don't Despair, Repair Deep Conditioning Mask (£30) as a weekly deep clean. I think my hair thanks me for it by staying pretty.