Chromonychia

Chromonychia is the presence of abnormal nail color. The natural nail plate is translucent and derives its apparent color from the underlying structures. Certain internal diseases and medications can cause color abnormalities in the nail plate. External factors can stain and discolor the nail plate. When the pigmentation is caused by external factors, the change in pigmentation parallels the contour of the proximal nail fold and, when caused by internal factors, the change usually follows the lunula contour.