Rainbow Lost Color

[SPM]

Good evening
This is my first post.
I need some guidance, one of my red rainbows lost all of its color overnight. He also appears to have labbored breathing.
I have a 50 gallon cube with a solid mix of tropicals. He seems to be the only fish in distress.

 

[jrd77]

What are your water parameters (Ammonia, nitrite, Nitrate, pH, temperature)?

 

[SPM]

Water is perfect, fish is deceased.

 

[jrd77]

I'm so sorry! Do the rest seem to be okay still?

 

[WILDER]

Sorry for your loss, check water stats again as heavy breathing and going pale is due to stress.

 

[SPM]

The water stats are perfect. All fish seem to be doing well.
I wonder if the platty babies had anything to do with it?

Thanks for the support and guidance!