Purple fringing
In photography (particularly digital photography), purple fringing (sometimes called PF) is the term for an unfocused purple or magenta "ghost" image on a photograph. This optical aberration is generally most visible as a coloring and lightening of dark edges adjacent to bright areas of broad-spectrum illumination, such as daylight or various types of gas-discharge lamps.
Lenses in general exhibit axial chromatic aberration, in which different colors of light do not focus in the same plane. Normally, lens designs are optimized so that two or more (at least three for apochromatic lenses) wavelengths of light in the visible spectrum focus at the same plane.