Not an abnormality at all. A. rivulatus, by far the most common green terror you'll see, originates from Ecuador and naturally comes with either white or orange edged fins. (Opinions differ on whether these represent different populations of the Ecuador species.) At one time you were just as likely to find white edged rivulatus, but the more colorful orange/reds have become more common, no doubt because people like the color.
As indicated in Stanzzzz7's post, there's a related fish, much rarer, A. stalsbergi from Peru, also with white edged fins, but its scales on the body are different-- rivulatus have light scales with dark center markings, which form horizontal rows; stalsbergi have light scales with dark borders. These fish were once confused and you can still find (usually older) photos of stalsbergi captioned as 'true' or 'real' rivulatus-- they're not. In reality they're easy to distinguish once you know what to look for.
There's another similar fish, A. blombergi, also from Ecuador; I've never personally seen blombergi for sale in this country.