What causes little boys feet to be yellow on the bottom? I was putting on my 5 year olds socks this morning and noticed that his feet were yellow on the bottom. I asked him if he had done a project with paint at school and he said no. I even had my 8 year old look at them to make sure I wasn't seeing things. It looks like the were completely stained yellow, only on the bottom. Anyone have a guess at what this might be? No he is not an alcoholic at 5.