I love your fishies and thanks for posting pics tracking their changes! I didn' realize they changed. From yours I think the ones i just got [i think they are both marbles] will only get more red/orange and light blue.
I think they definitely could change, take lots of pics cause it can be pretty subtle sometimes ^_^ Gilmore is kind of dark coppery/greenish/white. Kenickie used to just be black and white but he's been getting a bit of greenish iridescence too. believe it's just a specific type of black that's infertile, think it's melano, but I wouldn't quote me on that, lol