What about colour variation? It's plausible that, say, an alien who came to earth wouldn't be able to recognise facial features and/or mannerisms, but presuming they perceived colour in the same way as humans, which most seem to in fiction, shouldn't they be able to differentiate between various ethnicities, or even hair colours? And by extension, why is there never any colour variation in aliens?
What about colour variation? It's plausible that, say, an alien who came to earth wouldn't be able to recognise facial features and/or mannerisms, but presuming they perceived colour in the same way as humans, which most seem to in fiction, shouldn't they be able to differentiate between various ethnicities, or even hair colours? And by extension, why is there never any colour variation in aliens?