i was always told they are somewhat of a chameleon not taking long too change colour to suit there surroundings im not saying it happens in minutes but maybe days, i think if a blackie comes from the sandy beach and then proceeds through the lake and then stays there for a few days i think they start to change colour and vice versa. there are so many sheens of colour on different blackfish from purple to bronze and even greenish tinges but i dont know why some of there fins have a reddish hint to them???
see the red in the fins these were caught in sydney harbor