Clowns fighting with new LEDs... VIDEO

This happens with the percula's in my tank too. It's not every night but I suspect that the abrupt change in color spectrum does make the other fish appear differently. Your fish probably actually are turning blacker when their fighting. They darken up when their stressed. The battles will taper off if you keep up the lighting schedule. Mine still go at it maybe 30% of the time the lights switch. Whats funny to me is that night time is the only time my male perc gets brave with the female. She'll try to charge and he'll turn on her real quick and give her a weak snap. She's a good sport and they always end up shimmying it out though.

 

That's crazy.