Discoloration on IPhone13 Silicone Case Chalk Pink

I have purchased either the white or chalk pink silicone cases for all of my iPhones. I recently purchased an iPhone13 in June and got a brand new chalk pink silicone case. After a few weeks, it had stains on it and was discolored. I purchased another chalk pink case in October. I used it for one week and it has stains all over and discolored again! I used my iPhone 8 and iPhone 11 chalk pink silicone cases for many years and never had stains or discoloration on it. Is this a new material? What is causing the color change? Apple says it can be wiped off with a soft cloth but nothing works to get the stains off. Is anyone else experiencing this?