Ocellarus clowns 3rd white strip a dark grey???

Ok so I noticed that one of my clowns white strips has turned a dark grey, its the 3rd white strip by the tail. He is acting normal eating swimming happily nothing out of the ordinary other then this dark greying of his strip. kinda looks creepy as if its rotting off, but not. I will try and get pics but all I have is phone camera and it keeps getting way to blurry to see Just wondered if anyone knows what this would be or if this is really nothing to worry about. I had a bout with ich not long ago and treated everyone with cupermine, maybe that was it?