I've had a betta, named Joey, for a year now but I'm not sure how old he is. For the last few weeks his colour has been fading from dark blue to pretty much all white.
He hides at the bottom of the tank under a moss ball. I have to encourage him to come out for food and then he floats to the top. He struggles to swim back down again to his hiding spot but he does it. He's only about 5% active as he used to be.
He has no common illness symptoms either.