Perhaps those who wish to include animals under a discussion of complexion are native speakers of a language other than English.  American English never uses the term complexion for animals.  For them, we speak of skin color, scale color, color of feathers, fur, or even exoskeleton. Complexion is a term reserved for human beings. 

 On a different note, those seeking help with complexion problems may be interested in a number of different articles at  , where they can read further about human skin tones, recommended clothing colors, and about causes and solutions for complexion problems such as acne, oily skin, dry skin, wrinkles, rosacea, etc.  
  annaelena8