Salt Landscape

I am always so intrigued by the colors that come out when salt is used as this painting was done entirely with Payne's Grey. But right at that point where it transitions from the solid bleed to the salted area there is what appears to be another color. I wonder if it is impurities in the salt or water that cause this? It really seems limited to that area & I can assure you that my brush did not dip into another color for that section so what is going on? I don't know. Any insights would be appreciated. Happy Thursday Y'all!