The reason why the original image will turn green when using the watercolor filter is because of the way the watercolor filter is handled. According to relevant public information, watercolor filter is realized by simulating the effect of watercolor painting. In watercolor painting, the colors between pigments will penetrate and blend with each other to form new colors. Therefore, in the watercolor filter, for each pixel in the original image, the algorithm will mix the colors of the surrounding pixels to form a new color value.