Betta Fish: What is this? Is Aura okay?

I noticed about a 2 months ago he had some discoloration. I panicked and of course did a bunch of research to rule out any possible common illness or disease. There have been no changes in his behavior (hes still stubborn, active and silly). I did introduce him to a nerite snail and there was a piece of decor in his tank that i didnt realize was sharp (i sanded it down so its smooth on the edges). That barrel in the photo he loves to lay on and ive noticed it does touch that area when he gets comfy. Could that also be affecting anything (he loves the barrel and to just poke his head out at me) Ive been keeping an eye on it and it doesnt seem to be spreading. I just want to make sure hes okay