Thank you! Very fascinating. You have nice fish. Can’t go wrong with blue in my book!In general, it seems the classic kois that are cellophane based with red, black and yellow keep their patterns better while they mature. Kois with a lot of metallic/steel blue turn more blue as they mature. From what I’ve seen a good amount that are mostly cellophane when bought will have less and less cellophane as the color of their patched spread in. I’ve never had a koi’s color fade, only darken.
Here’s my old breeding “galaxy koi” HMPK when I bought him and then when he was older.
Here’s a few of his sons and their color change.
Then there are tiger kois, they seem to hold their colors better but that may be because they are also more of a “classic” koi coloration with black, red, and orange with little to no blue/metallic scaling.