Some times you have to wait a little while to get a reply. Your Festae looks great to me. Mine would change colors a lot too but I never had one in a solo tank. How big is he? Where is your tank located? There could be something startling it if your tank is near a busy part of your house. These guys are good for changing colors when angry, stressed, or ready to breed.
Dude, it's been an hour, give it time...same goes with the fish. It looks fine to me, but checking your water parameters probably isn't a bad idea if you think something is up.
He is about 8 inches hes in my living room. Hes usually a nice green fade to yellow. Or solid gold with black bars. lately hes been staying his golden color and stacking all the gravel in the corner of the tank. Nothing has really changed.
There's nothing wrong with him then. As long as you are keeping up with water changes and feeding him properly, he's fine. He's just getting older and larger. He probably wants the female that you're trying to find for him. BTW I wouldn't put a female in a 55 with an 8" male. During breeding they can get very violent. The female (or male depending on size of mate) will need a place to hide when things get too rough. There's not much room for a hiding place or a divider in a 55 for Festae of that size.