There are some symptoms that are never recognized in people with darker skin because specific-colored rashes or other skin issues may look different on different skin tones, but most medical school examples will have only shown what it looks like on fair skin. A close friend of mine was recently diagnosed with an immune disorder characterized by rashes in a specific shape/color, and she is less likely to receive timely diagnoses and treatment because most medical providers do not know what other symptoms to look for if they can't see the rash early on. So it was recommended to her, by her primary care doctor, that she look for a specialist with a skin tone similar to her own.