It really does seem as if they never sleep...they're always on the go when the lights are dimmed. I've lingered around and stared at my tank for hours during the night, being most of my fish are nocturnal this is the best time for me to observe and enjoy them...and it's always the same, the iridescents never hover in the same place for more than a second or two.
Sofia...I just thought of something, maybe he came all funny colored because of the movement or change in environment, from placing him into a bucket then to another tank. Maybe the temperature, or could be any number of things, gravel color like you mentioned? Maybe the other fish in the tank you placed him in after the bucket made him feel more comfortable. I do hear that they like company, preferebly of their own kind but you'll never know. Just some suggestions. I've never tried moving my sharks to anywhere...but I'll bet anything that they'd probably have some sort of reaction to it like yours did.