Brown black pigmented nail bands (melanonychia) can be a sign of subungual melanoma. This case report describes a child with melanonychia mimicking melanoma caused by green slime. Presumably, the slime embedded in the Melanotic macule of nail unit and its clinicopathologic spectrum ScienceDirect Pigmented Nail Disorders Basicmedical Key This dark line or discoloration on the nail can be a common condition called melanonychia, basically, extra pigment in the nail plate. In many people, especially those with more melanin in their Nail Matrix Nevus Springer Nature Link Melanonychia Striata Longitudinalis (MSL): Pigmented bands Academic Dermatology of Nevada