The light falling on a scene always has a predominant colour, such as yellow in the case of the sun, or an orangey hue in the case of tungsten bulbs, blue in the case of a cloudy sky or green in the presence of neon lighting. The human eye does not perceive this colour shift as the brain corrects for it. This is not the case for your camera... But don't panic: you can compensate for this using the colour balance (white balance) setting! Your picture will then appear as though lit with a neutral light source.