Kaposi’s sarcoma: A relatively rare malignant tumor characterized by spindle cell proliferation and angiomatous structures, the development of which may be associated with infection by herpes-like viruses. Kaposi’s sarcoma typically occurs in older men, especially in Eastern European populations, but there are also many patients in Asia. The skin is the most common organ affected, but internal organs may also be affected. Kaposi’s sarcoma can be classified into four major groups based on clinical features and epidemiology: classic, African, AIDS-related, and immunodeficiency. Typical Kaposi’s sarcoma occurs in the skin of the lower extremities, while AIDS-related Kaposi’s sarcoma occurs in the trunk. Dermoscopy is a non-invasive instrument that allows observation of microscopic structures and clinical features of the skin, especially pigmentation and vascularity, that are not visible to the naked eye, such as the epidermis and dermis. It can increase the diagnostic accuracy of various skin lesions. Therefore, we often use dermoscopy for further preoperative examination of patients. There are several features of Kaposi’s sarcoma under dermatoscopy, including dark violet-blue surface, scaly surface, and brown vesicles, which may be seen in other skin tumors and have less diagnostic value. Usually, the color of tumors seen by dermatoscopy does not differ much from the color seen by the naked eye, but we found that some parts of Kaposi’s sarcoma appeared in a rainbow of colors under dermatoscopy, a phenomenon that we had not seen before. Later, we observed several other Kaposi’s sarcoma patients and found that some of their lesions also appeared iridescent on dermatoscopy. We also found that the vascular structures underneath the lesions were denser in the areas where rainbow features were present and sparser in the areas where there were no rainbow features. Therefore, the rainbow phenomenon may be associated with the dense vascular structure underneath the lesions in some areas of Kaposi’s sarcoma. Over the years, we have used dermatoscopy to observe various skin tumors other than Kaposi’s sarcoma, including cutaneous hemangioma, melanoma, basal cell tumor, squamous cell tumor, etc., but no rainbow features were found in these tumors, so the rainbow features are likely to be a specific dermatoscopic feature unique to Kaposi’s sarcoma. Although skin slide pathology is still the most accurate method of diagnosing Kaposi’s sarcoma, this invasive test can only evaluate a small percentage of skin lesions and requires a multi-day wait for results. Based on our years of experience with dermoscopy, we believe that this rapid, non-invasive test is an important finding that allows dermatologists to quickly diagnose Kaposi’s sarcoma from its unique iridescent features. Although Kaposi’s sarcoma is a relatively rare disease, in severe cases it may involve internal organ lesions. People who find dark purple-blue tumors on their lower extremities should consult a dermatologist for further diagnosis and treatment.