Clownfish changing colour ?!

[JackPinny]

About a week ago I purchased a pair of juvenile clownfish just the plain orange type however they have started to change colour and are getting a lot darker.
I had the same problem with my last pair which almost turned into mocha clowns which is not a look that I like.
I am wondering whether this is something wrong with my tank or is something that can just happen.
I will attach some pics

This is before :

This is after :

 

[Sharkbait19]

They look happy and normal to me - the paler orange is can be due to stress. My standard occy went darker like that too (and my mocha went full black).
Fish will change colors to match their surrounding though - darker rock and backgrounds will yield darker colors.

 

[Rick's Reviews]

I'm no fish expert in the slightest but from your pictures your clownfish have some missing pieces.
I assume some kind of diesease or something eating them
Deffenitly not good so hopefully others will help

 

[Sharkbait19]

I'm no fish expert in the slightest but from your pictures your clownfish have some missing pieces.
I assume some kind of diesease or something eating them
Deffenitly not good so hopefully others will help

I had taken that for the angling of the picture, though I can see where there would be bites. In other shots (which I’d guess were from the same time) the fins look right.
In the event of bites, it would likely be due to the clowns fighting - unless there is a more aggressive fish in the tank.
Colors still look right to me though.

 

[Rick's Reviews]

I had taken that for the angling of the picture, though I can see where there would be bites. In other shots (which I’d guess were from the same time) the fins look right.
In the event of bites, it would likely be due to the clowns fighting - unless there is a more aggressive fish in the tank.
Colors still look right to me though.

Which would be great information for colour changing of clown fish in an established aquarium over many months/ years.
.. however in my opinion from the pictures provided these are not bite marks, looks like fin rot... But again I'm no expert.

This is not the usual body of a fish that has been bitten/ in my opinion