Clown tail stripe turning black

[CoralBeauty13]

Is this normal? It's been going this way for about three months. Nothing seems out of the way, just curious.

 

[davocean]

First time I've ever seen this.

 

[CoralsAddiction]

That black tail stripe is common among Solomon true percula clowns
You can see in the pic below the clown on the left has a dark grey/black tail stripe

 

[CoralsAddiction]

I can think of age, foods and host coral affecting the color of the clown in your case. Here's one I had with a tail like that