They are known for having a genetic trait that led to the blood disorder methemoglobinemia , causing the skin to appear blue. Leah Lefler What Caused the Blue Skin Color? The Short Answer The blue skin was caused by a diaphorase deficiency that led to methemoglobinemia, a rare condition that causes elevated levels of methemoglobin, the form of hemoglobin that cannot bind to oxygen. The Scientific Explanation.