What Causes Discoloration Of Skin On Abdomen During Detox Bath?

During a detox bath the skin on my abdomen turned green when it was exposed to the air. Then it appeared normal when immersed back into the water. The bath contained a filled tub of water and 1/4 cup each of the following: baking soda, sea salt, Apple cider vinegar and Epsom salts. I ve taken this bath many times and this has never happened before. Please tell me what this means