I did use TD in this batch. The FO is Nurture's Star Showers, which is non-discoloring. Soap base was OO, palm, coconut, shea butter, and castor.
I thought gel was helpful for brightening colors. I didn't realize it might darken my whites.
I had this recently happen to me. The FO was Barbershop 1920s by RE and I had previously done two loaves with Red, White and Blue and they turned out beautifully even though it has 0.2% Vanilla. Then I got a new Column mold and decided to do a 'lollipop' swirl with it and noticed that the white had discolored.
Wasn't sure what the difference was...same recipe, same FO, same colorants. Admittedly it was a new mold, and since I was leaving it in the kitchen, I covered the top. Earlier this week I was moving some inventory around and found a bar of the Barbershop I had made last year and compared it to the new bars and noticed that the Red and Blue of the new soap was a deeper color and then it dawned me...my soap had gone through gel.