Because of the high pH of the real soap that "WASH" is, it should scientifically have a significant impact on color loss.
Some stylists and home users have told us otherwise, but because of the basic chemistry facts, we are skeptical. As a matter of fact, some people who use vivid hair dyes (bright reds, etc.) use WASH to get the color off their hands if they haven't worn gloves or the dye has gotten on their hands. We've seen that with my own eyes, and WASH really works, confirming our advice to avoid WASH on color-treated hair.