well, I thought so as well... before that, I always used a soymilk shampoo that was rather expensive. It wasn't specially designed for hair systems but it was sulfate-free and colour-saving. Was quite okay, had no issues with that. Then, when at our local hair store that shampoo wasn't available for a while, I tried two special wig shampoo. HORIBBLE! Ruined the colour and made the hair brittle - wouldn't have expected this from expensive wig shampoos like that. Well, bad luck...
So I FINALLY went to a simple drugstore after reading a lot of reviews on the web concerning shampoos for coloured hair. After trying one Schwarzkopf product which wasn't so nice to the colour, I ended up using a product by a brand called Dove, 4$ a bottle for 6-7 weeks or so. With this I am so positively surprised
Even after 4 months, my wig hair has kept 95% of it's original colour (dark brown), no red tones at all (as I had it before with other shampoos), it still looks quite shiny and feels nice. Still, there might be one downside: Not sure if this shampoo is to blame, but for some reason my favourite tape won't stick to the swiss lace any more. I had to change to a different tape then...
Finally, the very first shampoo I had is available again, and I'm gonna try this on my new wigs.