Indoor photography using a flash can be misleading. Outside pics in natural light are better but depending on the amount of sunlight and time of day colours can still look vastly different from pic to pic. Great examples: Bare aluminum can appear to have a bluish hue at high noon on a bright clear day or a bronze hue around sunset. Sky, the British under surface colour, can look lime green, blue-green, or yellowy green depending on the light source.
As Greebo says, dirt and weathering effects on a skin can change the hue as well. Paint colours on a 'clean' skin will look different than on a 'dirty' skin.
