Why does turmeric stain become red on apply in soap?

Turmeric contains curcumin, a pigment that can appear yellow in its natural form. When turmeric is applied to soap, the alkaline environment can cause a chemical reaction that alters the structure of curcumin, resulting in a red or reddish hue. This transformation is due to a shift in the pH level, which activates the pigment's color-changing properties. Thus, the color change is a result of the interaction between the turmeric and the soap's ingredients.