This issue is mostly about what kind of light source you are using. Tungsten lights have a very yellow colour cast. Flourescent light is on the blue side and so is strong sunlight when the model is in the shade. It is good to have a 'daylight' bulb for a light source, not only for photographing your models but also doing your modelling. If you don't adjust your camera settings for different light source, colour balance can also be altered when processing your image on the PC after uploading from your camera. Most image editing software will give you options to change this, but don't go overboard
Cheers
James