I am at work and have a very small laptop so the pictures are'nt that clear or big. I the betta is less then a year it is possible it is coloration that is now showing. I not it could be finrot, usually from poor water conditions or ammonia poisoning (this is usually more around the gills and on the body more then the fins) or it could be both. Like I said I dont have a clear pic but those are posibilities. Did you check your water parameters? Is this betta in a cycled tank or uncycled?

yes everything is cycled. All my bettas are kept the same way. It appears to have developed within a day because these "markings" weren't there yesterday or I would have seen them when I looked. (I look at them all in the morning before I leave :)

Nothing looks like its disease or fraying - it looks like normal sort of coloration. I've had red bettas where the edges of their fins are blue - so I can easily see your betta having the same sort of coloration.

??

How long have you had it? It does look more like coloring, especially the last pic. As long as the fins aren't fraying and the fish appears "happy" and water parameters are good, no worries. Could be just good living and eating brought out the colors. Alot of fish food now in engineered for color enhanceing with the right blend of nutrients.

I will keep an eye on him for the next few days just to be 100% certain its just a changing of coloration. Will post if anything changes.

thanks to those of you who responded :) much appreciated.

the betta in question has deceased :(

I'm really sorry!!

But I don't think it had to do with the fin coloration. Truly, from the pix you put up, the fins seemed perfect, all intact. And if you hadn't said there was a colour change, I would have thought that was just the coloration of the betta.

It wasn't really noticable from the pic cause his fins were folded but there was an extremely slight amount of decay on the anal and caudal fins that wouldn't have been noticed by most, but when he was flaring at his neighbor and the fins were spread out I was able to see the missing "ends". It is really hard to get good pics of these guys! :/