Betta fish looks like internal bleeding

[c10v3r53]

I need help my fish looks like it has internal bleeding I have no idea what happing his acting fine eating and very active. PH is fine no idea what the am and nit is I have had the fish for 3 month I just did a full water change keeping 20 percent old water and filter his the only fish in a 3 gallon tank with filter he eat brime shimp once a week and eats omega one betta buffet flake tank is 3 month old like the fish I bought aquarium bacteria only use once a month called marineland and his got a big allgate tou and a leaf in the middle glass part and he got a heat at 78

 

[Delapool]

Hi, I can’t see anything that I couldn’t put down to normal colour. Are the scales standing up or looking ruffled like dropsy? Also how quick was colour change?

First thing would be to take some water to fish store for checking ammonia although should be cycled after 3 months.

Generally colour change is either natural (can be quite quick or store was feeding colour enhancing foods), burns eg ammonia or bacterial infection.

 

[King Fisher]

Could be the beginning of red spot disease. If that's the case the red spot you see now will turn into an open sore.

But given that he appears to behave normally then I'd say it could be color change as Delapool pointed out. Also, your fish seems to have red in his face as a natural color so red appearing on his body could be him maturing into his natural colors??