Background Non-organic vision loss can manifest in various ways, most commonly in the form of reduced vision and visual field defects. Colour vision disorders in the context of a conversion disorder have only rarely been reported. Materials and Methods This review presents the case of a 9-year-old boy with a colour vision disorder as the isolated symptom of a conversion disorder. The challenging in this case was an additional somatic comorbidity – a congenital red-green deficiency. Consequently it was difficult to make a diagnosis and to convince the parents. Conclusion It is important to rule out organic causes and establish the diagnosis of a conversion disorder. In these cases, multidisciplinary treatment is crucial for a successful outcome. The diagnosis may be especially challenging when the patients have both somatic and psychogenic complaints.