It was stated that Guo Jing shaved his head to disguise himself as Yideng when Yinggu came to attack.
So, did he wear a wig after that? Did he roam jiang hu with his shiny scalp? Huang Rong must have thought he looked ridiculous. Furthermore, I'm pretty sure the novel art that appears at the beginning of each chapter showed Guo Jing with a full head of hair.