Gills are turning grey!

[Campbell]

My male betta is turning grey right where his head connects to his body on both sides. Could this be from to much flaring? He is also acting lethargic and staying toward the bottom. He is normally rather aggressive and energetic. The last water change was 25% two days ago. 5 gallon, uncyled, 78-79 degrees in the tank. He's been in there for about 3 weeks. He is eating normally though. I have covered the tank with a towel in hopes it will prevent him from seeing his reflection. What can I do and what could be the problem.