I'll take a stab at this.
In the wild there are many marine fish with color markings outside the norm. For example, do a google image search of "white yellow tang". Fascinating color morphs can be seen. 10 years ago, a LFS here in St. George had a Yellow Tang with white markings. It was in their ~400 gal display tank for quite a few years. Unfortunately, that store was sold and has since folded.
I agree with Marcos. There is no doubt that interesting color morphs of many types of Clownfish have been collected over the years, but not until the development of reliable large scale breeding could anything be done with those rare morphs. In the wild, less than 1% of clownfish eggs reach adult. That's a lot of color morphs that went unseen. On the other hand, with captive bred clownfish survivability near 95% these days, the breeders get to play with selectively breeding a lot of different color morphs.
Since then I believe there have been several dozen generations and some of the Lightning Maroon offered today are even sweeter than the original. Did you know that out of each batch from a pair of Lightning Maroon Clownfish, only about 20%(?) of offspring have the lightning markings. The rest all look like normal Maroon Clownfish. I believe the reason is genetic.
Shaun Sabey is our local breeder/expert. Maybe he will chime in here.
Aloha,
Mark

P.S. One more link, from 2012, for all clownfish aficionados where breeder Matt Pederson clarifies a few things: