Colour does not so much wear off as wash out. Every wash swells the hair shaft slightly and lets pigment escape. Most of what extends the life of a colour service comes down to washing less aggressively, less often, and in cooler water.
Wait before the first wash
Give fresh colour at least forty-eight hours before it meets shampoo. The cuticle needs time to close, and pigment lost in the first wash is pigment that never had a chance to settle.
Turn the temperature down
Hot water opens the cuticle. A cooler final rinse closes it, which both keeps pigment in and leaves the hair noticeably shinier, because a flat cuticle reflects light more evenly.
Sulphates are not the enemy, but they are efficient
Sulphates are effective surfactants, and effective is the problem: they strip colour along with oil. A gentler surfactant system cleans slightly less thoroughly, which is exactly what you want on coloured hair.
Heat and sun both fade
Use a heat protectant before styling, and drop the iron temperature — most hair does not need the maximum setting. UV fades colour the same way it fades fabric, so a hat on long summer days does real work, particularly on reds, which fade fastest.
Between appointments
A weekly deep conditioner or bond-building treatment addresses the structural side rather than the colour side. Colour-depositing conditioners can top up tone between visits — introduce them gradually, as they build.