A black mug with a green border is a ceramic or glass mug with a black exterior and a green rim around the edge of the mug. The green border can vary in width and style, from a thin, subtle line to a broader, more prominent band. Black mugs with green borders are often used for drinking hot beverages such as coffee or tea, and can add a stylish and contemporary element to a kitchen or dining room decor. The black colour and green border can also create a bold and eye-catching contrast.