1. An apparatus for controlling gain of color signal, comprising: an auto white balance algorithm applying unit determining a white estimation region from an input image, and calculating a first color signal gain for correcting an average color signal level of pixels of the white estimation region to white; a pixel determining unit determining a form of each pixel according to brightness and color using the color signal level of the each pixel of the input image; and a color signal gain determining unit determining a color signal gain to be applied to the each pixel according to the form of the each pixel of the input image as any one of the first color signal gain, a second color signal gain determined by the color signal level of the each pixel for correcting the each pixel to white and a unit gain.