Marble gene bettas (not all marble color have the marble gene) are awesome!
See the blue betta and the white/black betta next to it in my signature? Those are the same exact betta. He changed from royal blue to pure white, then to white and red, then finally mostly black with some white and red before he passed away. I never knew about the marble gene until he started changing colors and we spent a few months trying to "cure" him to no avail.
If yours has the marble gene, I suggest taking photos every so often, because comparing them the before and after photos is really fun!