A 22-month-old girl is referred with a persistent colour change in a patchy distribution over her body. She is otherwise well and fully vaccinated to date. She was born post-term at 41 weeks’ gestation by normal vaginal delivery. Her mother reports that she had a blistering skin rash at birth and a ‘high white cell count’. She was treated with antibiotics for one week on the neonatal unit and had extensive tests to rule out viral illness, all of which were negative. Her mother shares neonatal photos and is certain that the areas of colour change do not correspond with the areas of previous blistering.