He must be at least something like 2 years old by now.
He should be completely colored
Your water-conditions are OK I assume?
Your tank wouldn’t be overcrowded?
The size of the tank is appropriate ?
He is not being harassed too much by other fish(if there are any) in the tank? If so, he could behave like a subdominant male if that happens to be the case.
All these topics (or a combination) could lead to some sort of stress which makes him lose his color.
I’m not questioning your knowledge about cichlids but just incase, are we talking about the same Red Empress? Protomelas taeniolatus.
Before I bought mine, 5 weeks ago, I did some research and what I’ve read about them, they shouldn’t be that much of a chaser. They even try to avoid any confrontation with others, as much as they can, and that is exactly what I see in my tank (till now). When he gets fed up with other fish irritating him, he just open his mouth and they’re gone. It’s the only “non mbuna” in my mbuna tank because of their similar dietary needs. They are considered to be easy, peaceful and non territorial.(except during spawning, they need some space of their own)
I’m not sure any of this will bring back the colors of your Empress, but perhaps you could look at some of the points I’ve mentioned.
Jimmy