Colour change or something sinister?

[Deeznuts]

I believe the black on the koi is just a colour change as it’s happening slowly and the koi is eating and behaving fine. However, just to be certain, I’d like other people’s opinions.

I have looked online at possible diseases and none look like this.

 

[Colin_T]

Just looks like colour to me.

 

[Deeznuts]

Okay, great. Makes him a lot uglier than before lol.

He's the only one turning that colour. I wonder if it's parent's genes weren't that strong.

 

[Back in the fold]

He’s growing and his color is changing for that reason . Another year or two he’ll look even more different .