Fin Discoloration (?)

Hello! I am fairly new to the site, and I am not wholly sure if this kind of post can go here, but I was worried about something that I am noticing on my Betta's tail. His name is Dmetri, and he is almost four years old (or three and a half, depending on the estimate). He is a veiltail, and he lives with me in my dorm room. He is eating well, and is somewhat active. He tends to lounge near the surface of the bowl, and then dart in and out of the silk plants and rocks. That behavior is normal, from what I can see.

Despite this normal behavior and appetite, I am noticing a little bit of discoloration on the long fin right before his tail (I believe it is called the pelvic fin, though I am not certain). At the juncture where the fin connects to his body, there is a slight amber color that I don't recall seeing before. Is there anyone who might know what this is? I have included some pictures to illustrate what I am trying to say. I edited a few of them to try and make them clearer, because it is hard to get a good shot of the little guy. The fifth picture shows it best, I think.

Thank you for your help and time!