Help explain fish with discolorations.....

[bettasngoldfish]

You bring up a good point Meyer. I'm not sure koi change color when stressed or ill (I have never had koi) I know for a fact that goldfish and bettas lighten when stressed and cichlids will actually darken. So it depends on the type of fish I guess.

 

[Meyer Jordan]

Not sure if this really sheds any light on the topic, but it is a very interesting read.
http://www.raingarden.us/color.htm