Greetings to the forum members.
The topic seems to be repetitive. What could be the reason for discoloration of a liquid soap with Sodium Laureth Sulphate as the primary surfactant ??? The surprising fact is that there is no discoloration when the liquid soap is filled in HDPE canisters whereas when filled in transparent PET bottles the color fades within a week and completely vanishes within 2 weeks. The colorant is Carmoisine 25% which has been used in other products without any difficulties or discoloration. The fragrance could be a possibility for discoloration but how ??? Another common reason for discoloration is pH level but in that case discoloration should appear in all types of packaging be it HDPE or PET.
The diagnosis and troubleshooting of this issue should be an easy task for an expert chemist but lack of formal training renders it a mysterious expedition for a novice.