Regarding tortoiseshells vs. calicos, the term "calico" is hardly ever used in the UK and cats that are ginger, black, and white (or similar colouring) are generally just referred to as tortoiseshell or tortoiseshell-and-white. I think "tortoiseshell" is sort of an umbrella term, but also refers more specifically to a mottled black and ginger cat. I'm guessing this is why the Erins have never, to my knowledge, referred to any of their characters as calico, as the word is mostly only used in America :)
I imagined Longtail as being white, or very pale grey, with black stripes.
It was only when I started seeing fan art of Yellowfang that I realised she was portrayed with a flattened face. Before that, if anyone here ever played the PF. Magic Catz games, I imagined her as a grey version of the Alley Cat xD