1. A color detector for a vehicle that detects a color of an external image by receiving predetermined image data from a camera photographing the external image of the vehicle, comprising; an RGB converting unit converting a photographed image of the camera into RGB image data; an HSI (Hue, Saturation, and Intensity) image extracting unit extracting a hue image, a saturation image, and an intensity image of the RGB image data; a reverse image extracting unit extracting a reverse saturation image, a reverse modulo saturation image, and a reverse luminance image of the RGB image data; and a color detecting unit detecting white, black, red, and yellow colors by using two or more images selected from the hue image, the saturation image, the intensity image, the reverse saturation image, the reverse modulo saturation image, and the reverse luminance image by a predetermined algorithm.