Need some advice!

So i wore this for the first time a few weeks ago in Mexico. After the first time wearing it purple splotches started appearing. I assumed I spilled something so I cleaned it off and didn’t think again. Later that night it dried and had the purple again! I keep washing it out and have used cold water w laundry detergent and it will come out and look perfect but then be back. Has this happened to anyone before? Advice? Btw I swam In same water other days in white and no purple on those