Oh my goodness, what a find!! Hes absolutely stunning! And what a cute face and adorable little blue eyes! <3
Oh, the color changing is very normal....its commonly refereed to as 'Marbling'. Paler bettas with little sports of color like yours, or sometimes even with no visible spots of color, often gain more color and change over time. Its a color gene variation.....like dragon scaling, as far as I understand at least. ;)
They can be quite fun. xD Some change so drastically they don't even look like the same fish after several months!