Fading of color in fish is usually a sign of stress or them 'sleeping'. As the later isn't the case here, your fish is stressed out.
Can you tell us more about your tank? Size, how long it has been running, how long you've had the emperor, other tank mates, and current parameters?
I can see small areas where the adult coloration may be starting but you can only assume that is the case after you have eliminated water quality or stress as the cause. We need a tank/ water report please