The second way is if the light source does not match the color balance of the film. Our brain is what adjusts them to look white, much like an auto-white balance in a camcorder. Film cannot automatically correct for proper color balance, so our pictures may have a color cast if we do not match the film being used to our light source. Daylight is approximately 5600 degrees K. Tungsten light, i.e. table lamps, gives an orange color cast to daylight balanced film. Fluorescent light will give a green color cast.
Some films come balanced for specific light sources other than daylight such as Tungsten.
If you cannot find film balanced for your particular light source, then you may need to use filtration in order to correct your picture so that it looks more natural. All of the elements will play some part in contributing to a photograph. If you find a picture you like, analyze all the elements. Once you recognize these elements, then go into a what if mode. Look at light in nature that intrigues you.