Our eyes compensate automatically for light sources of different color temperatures (e.g. sunlight, cloudy, fluorescent, and incandescent) but cameras can only report what they see truthfully! In order to render colors accurately digital cameras have a feature called white balance that corrects color casts.
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The white point in an image is calculated and the appropriate correction is made. This is done automatically or, on some models, can be done manually.
As with all user overrides, remember to reset it!
You can magically correct images later using the curves command in PhotoShop.