Pants are red, probably because some links in the dyeing process are not up to standard. Generally speaking, the dyeing fastness is not good enough. Clothing is "light-resistant, acid-base resistant" after dyeing. We wear clothes and sweat. Different environments lead to different pH values, and we often bask in the sun. Therefore, the color fastness of clothing is not enough, which will lead to the fading and discoloration of black clothing for one reason or another.

You can soak red trousers in strong salt water for 30 to 40 minutes. Pay attention to soak your pants completely in it and rub them several times without interruption. Then clean it normally and soak it in light salt water for half an hour. Wash it again, and the pants will change back to their original color.