Seeing in PA got me looking further. Blue is definitely seen in pictures of fish.
Years back I was in PA for a few years. One day, in a stream inches deep maybe 6' across. Found an albino trout. Small about 8" it was a vanilla color with pinkish eyes. Sat on the bank and watched it for a couple hours. Never saw such before or after. Remember wondering how well it could see. It was maybe 5' from where I was sitting. Holding behind a big rock. Appeared to be feeding. As every few minutes it would make a quick dart left or right. Yet didn't seem to care about me being close enough to reach out and grab for it. Though when I stood to leave. It was
gone in a flash. But back where it was before I took 4 steps.
There was a hatchery in the area. But this particular stream was not connected to release points.
I have never seen a blue trout. Such a creature would be perfect for the au bleu dish. In the blue trout recipe a very fresh fish is poached in vinegar etc. The fish slime and vinegar on a char, dolly, or brook trout makes for a very blue creature on the plate. These blue trout sound perfect for such a dish.