The Brains blogged how water alone is the greatest threat to colored hair. So- does using a color-safe shampoo really matter? Will it prevent fading any more than a regular shampoo? What about those color-care shampoos that are sulfate-free?
Nope! I once bought a sulfate-free color-safe shampoo from Enjoy, and it doesn't work any better than the huge bottle of Head and Shoulders I bought from Costco. I do find that moisturizing shampoos help keep the color looking better, possibly because your hair is shinier and glossier. But really, I've never noticed a difference from any of the brands I've tried. Those clarifying shampoos however, stripped a lot of color off, so don't get those.
And trust me, my hair color lasts. I have to since I dye them really bright and vibrant colors, and it costs way too much, and it's too damaging to do bleach them so often, so I do speak from experience. Dry shampoo/baby powders are your best bet to extending hair color.
I do believe the Brains did several posts on this, if you run a search. Water itself is the main reason why you lose color so quickly. Washing less often will prolong your color.