Chromatic Aberration is the bane of digital photographers. It can be seen as a halo or fringe around the edges of an object in a photograph when you photograph it in certain lights – you might see it for example, when you photograph a darker object in front of a bright sky. Some tools like Lightroom have settings that help remove chromatic aberration but sometimes it’s so obvious and so distracting that a bigger fix is required.
In this image (click to enlarge), the statue has a very obvious blue edge to it and not even Lightroom could fix this. The solution is to open the image in Photoshop and to fix it there.