i really think he looks fine. It his normal coloration. I think many blue bettas looks like that. How he acting? Is there any changes ? Don't worry that he don't make the bubble nest it not change to health problem.But is he darting, scratching? His fins looks fine the are not clumped . Is he less active? Sitting on the bottom of the tank longer then usually? Any other symptoms.
If he don't have any symptoms just keep eye on him . He looks fine.
Still trying to eat pellets and spitting them?