The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
I am sure it can vary in all places of the world. All trout take on different patterns, shades, coloration, spots and other various markings etc. This can all be due to the content of the water, temps, cover and a host of other variables.