Blue nevus
Blue nevus is a type of colored nevus, typically a single well-demarcated blue or black nodule. The blue color of the nevus is caused by the pigmentary cells being deep in the skin.

A biopsy is sometimes performed, or the whole lesion surgically removed. The clinical outcome is generally good and there is a small chance of cancerous transformation. Differential diagnosis includes dermatofibroma and melanoma.

  • Because the nevus cells are deeply present, it appears blue.
  • Atypical example ― Blue nevus usually has a symmetrical shape. Basal cell carcinoma and melanoma should be differentiated in such cases
References Blue Nevus 31747181 
The term blue nevus describes a group of skin lesions characterized by dermal proliferation of melanocytes presenting as blue to black nodules on the head, extremities, or buttocks. In most cases, they are acquired and present as a solitary lesion but may also be congenital and appear at multiple sites. Blue nevi are melanotic dermal lesions that commonly presents as a blue nodule on the scalp, extremities, sacrococcygeal region, or buttocks. Its characteristic blue to black hue is frequently confused with other darker pigmented lesions, including malignant melanoma.