Aberrations, or optical imperfections, exist because no lens is optically perfect. Almost all lenses show aberrations from the ‘perfect’ image.
Chromatic aberration
This is a lens aberration that produces colour fringing around the outlines of objects near the edges of the picture. It’s very hard to eradicate completely from lens designs without making them extremely complex or expensive, but it is possible to correct chromatic aberration using software and many cameras will now correct it automatically as they process the image.