MY BLUE FISH SIR HAD PINK IN HIS TAIL ALSO, WELL I MOVED HIM TO ANOTHER TANK SO I COULD TREAT A DIFFERENT FISH, WELL I MOVED HIM NEXT TO A FEMALE, HE IS NOW MAROON WHERE HE WAS BLUE AND RED WHERE HE WAS PINK!!!! IM CONFUSED IS HE SICK OR WHAT!?!?! IS THE WATER TOO COLD?!?!
Some betta fish will change color throughout their lives. It's called "marbling". One day your betta would be pure white, the next week there is a blue spot on his tummy, but later the fish could turn green, or fully blue, and back to white again! It's a gene that makes the fish just continue to change as they age..it's really cool :)