I went petco the other day and I noticed this Betta fish with a red and white patch on its head. It almost looks like the scales have been scraped off. I feel like he has body rot but I'm not sure, I've never seen this kind of thing before. I am tempted to buy him and treat him for whatever he has, I just need to figure out what that is. Hopefully the picture is clear enough for you guys to be able to tell.
Normally diseases in bettas tend to affect the fins/gills as well as the body. Looking at the pictures the fins look perfectly healthy. This doesn't mean that the fish definitely doesn't have a common disease but it can be safely ruled out.
Coloration Changes in Bettas
Why do bettas change color? Based on the picture that is the main question we are trying to answer. Bettas certainly change color from diseases but as mentioned above the fins and gills look perfectly fine. Three common things that cause bettas to change color are Stress, Ammonia, and rubbing into things. Rubbing up against things usually cause the scales to turn a silver color and not a red. Stress and ammonia burns also mostly cause the color to turn silver unless the betta has a red pigment under the skin. You can check for this red pigment by looking through the fins behind a light source to see if there is any red present in the fins.
Based on the information provided the most likely culprit is stress or ammonia burns or a combination of both. Ammonia is caused by dirty water or untreated water. While you can get medicine for both the cheapest way would to perform water changes using treated water and give the betta hiding places in the tank.