The Tornado doesn't have one - you just fill the bowl!
Yeah, this is pretty normal, just the effects of heat on the metal surface changing how photons interact and the frequency when it reflects them.
As far as I know this is essentially creating a layer of oxidised metal, and the type and quality of the metal, plus the temperature it's heated to, will create a different depth of oxide layer which causes the photons reflected off it to have a specific colour (frequency). It's due to the different energy levels of the outer electron shell of the pure metal vs. the metal oxide - the different materials have differing energy levels that create specific wavelengths/frequencies of the reflected light that effect the final colour.
A polish will abrade away the oxide layer to reveal the original metal surface, but the moment you heat it up again you'll return to the coloured appearance.
FYI: an IH will reduce this compared to a torch since the heating is averaged out across most of the vape head while a torch is of course concentrated at a small point so gets hotter before the heat conducts through the rest of the metal.
From what I've read, some gentle rotating doesn't hurt but is less necessary than with some other TED vapes, as the copper is much faster at conducting the heat to the rest of the device.
By the way, did you get hit by customs, and if so, roughly how much?