Black Outline Around Molly's Tail Fin

[molver]

Hello!

I just wanted to ask if it's bad when a fish has black outlines around its tail.
 
I notice them a lot at pet stores, and I avoid buying them. 

But I bought a Sailfin Molly last night, and just noticed that he has some black around the outside of his tail fin.
 
It's barely noticeable, but I noticed it, and now I'm unhappy.
 
He's still really awesome, but I was wondering what I can do to make the black go away. He's still a little shy (since I only got him last night), but I think the potential for him being active and happy is high.
 
I don't think he's sick, and I can't attach a picture because the outlines wouldn't show on the picture.

 

[attibones]

Well what color is his body? This is a common trait and usually should not present any issues. Is he eating normally? Pooping normally? Swimming fine?

 

[bluesword23516]

It can be his coloration.  Just keep an eye on him.  If he seems fine, chances are that is his coloring. 

 

[molver]

I guess it's his colouring. I was just wondering if there's anyway to make him grow out of the black outline.
 
He couldn't be better. He's a bright orange, and he has a blue sheen on his dorsal and caudal fin. I think he's absolutely beautiful. He even picks at my finger when I put my finger in the tank, and I only got him yesterday!
 
He's quickly becoming my favourite in the tank.