Which tumor type is associated with excessive production of melanin?

The tumor type associated with excessive production of melanin is melanoma. Melanomas arise from melanocytes, the cells responsible for producing melanin, the pigment that gives skin, hair, and eyes their color. This tumor is particularly notable for its aggressive nature and tendency to metastasize. It can occur in various locations, including the skin, mucous membranes, and even in the eyes.

In contrast, squamous cell carcinoma originates from squamous cells and does not have the capacity to produce significant amounts of melanin. Lymphoma, which affects lymphoid tissue, and osteosarcoma, a type of bone cancer, also do not involve melanocyte activity or melanin production. Therefore, the defining characteristic of melanoma's excessive production of melanin clearly identifies it as the correct answer in this context.