Light has a colour of its own: a bulb is warm and yellow, open shade is cool and blue, and daylight at noon lies between them. A camera corrects for this so that a white object comes out white. When the correction misses, every colour in the picture shifts together, and a cream sweater photographed under a lamp looks yellow.
For product photos the cast matters because shoppers judge colour from the image, and a product that arrives in a shade other than the one shown disappoints. Photographing near a window in daylight, with indoor lamps switched off, avoids mixed light. A sheet of white paper in a test shot shows the cast at once: if the paper is not white, neither is anything else.