Dr Marisa Rodriguez Carmona, Senior Lecturer in Optics and Vision Science at City, University of London, remembers a patient whose job was dyeing buttons. His employer had noticed that he was no longer matching buttons correctly to the clothing, so he was referred to City’s Colour Research Laboratory, where he was diagnosed with colour vision deficiency (CVD). A week later, the patient emailed to say he’d been diagnosed as diabetic – the CVD had been the first sign. He was then treated for diabetes, and made diet and lifestyle changes. A year later, when Marisa saw him again, his colour vision had improved.