I love your platinum butterfly - just beautiful ! I have a koi named Madame Butterfly, as she spreads her fins like a butterfly. As it turns out, Madame is a Monsieur , but I digress
When I purchased her / him, she was orange and black and not long after I got her, she literally turned white and black overnight !
I don't understand enough about koi, but think there is something called " beni" which is an underlying color, which will come out.
All my koi are standard fins, and they are hard on my plants.....so, maybe if I'd started with butterfly ( long fins ) I'd have had less trouble. I also wonder if the breed less with gold fish....I had a population explosion...which resulted in my rehoming all the goldfish.
Yesterday, while out walking, I stopped at a house I've heard has a koi pond, as I wanted to introduce myself and see if they need any koi babies. They were home, but didn't answer the door and I didn't feeling like walking to their back yard, looking like a pond stalker - ha ha!