White Balance.

This is the function that adjusts the video recorder to the type of light that enters the lens. It does this because light varies according to it's source. For example, tungsten light emitted by household bulbs is different from sunlight. You'll know that the balance is set wrong if an image looks too red or too blue.

Page 57, The video activists handbook.

To set the white balance you point the camera at something white before filming or use a piece of white paper.