Betta color change and fin rot; related?

I'm pretty sure these two occurrences are coincidence, but I'll throw it out
here for opinion anyway.

I have two male bettas. I've no idea of their exact age, but neither has
grown noticeably since I picked them up at the LFS in June. Each is in its
own 1.25 gallon bowl with about a half-inch of pea-gravel and a java fern.
50% water changes weekly (a 100% change two weeks ago).

Late last week one of the fish showed signs of fin rot, so I picked up some
Bettafix and have been treating him daily according to the instructions. He's
lost about a third of his fin and tail length. Fortunately, further
disintegration seems to have ceased.

Earlier this week, his original dark blue/iridescent green coloration started
to change to a deep red. This coloration change now affects large portions of
his ventral fins. It has also started to appear near his body's midsection.

These things aside, he continues to be an active swimmer with a good appetite
and, while changing, his colors are still strong and vibrant.

A few web and usenet searches have suggested that color change is a normal
part of the aging process, so I presume these two incidents are unrelated.
Or, have I missed something?

Incidentally, the other betta is fine. In fact, his fins look to have grown
longer compared to when I brought him home. However, I attribute that mostly
to his original housing--The classic "cup".

Tkx,
--Vincent