Technically, what is it? Chromatic Aberration is a common optical problem that occurs when a lens is either unable to bring all wavelengths of color to the same focal plane, and/or when wavelengths of color are focused at different positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colors of light travelling at different speeds while passing through a lens. More technical explanations can be found here.
So what to do? Google of course. In the upper end edit programs there are options to reduce the effects of CA. I found a nice little program as an alternative for low cost that worked as advertised. The program is PTLens. There is a trial time for 10 images. I picked my barn picture which had a lot of distortion between the building and sky - and I didn't notice but a lot of red in the foliage on both the right and left. I followed the directions and it worked great! I now have another tool for the tool box.
The before and afters:
With the Chromatic Aberration.
With the Chromatic Aberration removed.
Since the CA is caused at the time the image is taken, early removal would probably be best. In my barn photo, the CA on the barn didn't show up until I put it on a monitor as a screen saver. The it was painful. If that photo is going to go into a competition, I can't take that chance. One of those things that if it is not there, you'll never know, but leave it in there and .......