Why is my rainbowfish black???

I came home today to see one of my turquoise rainbowfish severely discolored. He's black and all the rest are perfectly fine. They're all undergoing the heat treatment for ich, but for some odd reason this poor fellow is changing colors on me! you can clearly see which one it is and how all the others are fine. I don't understand.

 

Wow that's weird. Other then his color he looks fine. What's your water parameters?

 

wow! That's bizarre.

 

I here hybrids of rainbow fish loose there color, but I've never seen a black one

 

Maybe you have a rare melanistic rainbow fish, I want it!

 

0,0, 40. Everything is normal. As its water change day.

This happened within 6 hours of me being gone. It wasn't a progressive thing.

 

Were the lights off when you were gone?
I've been reading on Google, and some people have rainbow fish that get charcoal grey/black during lights out or when mad, and usually color back up after a bit

 

How old are they (how long have you had them). Do you know which are male or female. At first glance I thought the lighter colored ones were female and your dark one was a male - in one of his moods you hadn't seen before. But looking at the dorsal fins I'm not sure the dark one is a male.

My males have always had more color variations (not just the nose but full body changes in color intensities).

Any other occupants either new or unusually aggressive?

 

No idea on the sexes, but I've had them for at least 2 months now. There's 8 total, I just added two new smaller ones, but no unusual or out of the ordinary aggression from the school.
The lights were on when I left. I noticed this after coming home from work about 2 hours before lights out.

 

There all bosmaini?

 

No idea on the sexes, but I've had them for at least 2 months now. There's 8 total, I just added two new smaller ones, but no unusual or out of the ordinary aggression from the school.
The lights were on when I left. I noticed this after coming home from work about 2 hours before lights out.

Is it still black or back to normal? It's really only an issue if it stays the pure black color

 

They're Turquoise Rainbows. And I'll have to see when I get back home Monday. Had to leave for a business thing.

 

Update: I returned home today, after turning my lights on he was black for some time but started to slightly color up. It's still obvious which one he is, but he's showing some color. I noticed His anal find look kind of tattered, nothing severe, but noticeable nonetheless.