I have 4 parrots and when I first got them about 4 years ago, they were all a dark color like a green severum. 3 of those parrots turned completely orange and they're awesome looking, but the other one never really changed so now he's half orange. Well, in the past few days, 1 of my orange parrots started turning back to the darker color. I thought it might have been ammonia burns or something but I tested my tank and it's at 6.6 PH, 0 Ammonia, 0 Nitrites, 10-20 Nitrates. Is there any reason for this parrot to be changing colors from orange back to a green severum color?