1. An apparatus for generating an ultrasonic image, the apparatus comprising: a sample image acquisition unit which acquires a sample image by photographing a portion of a skin of a pregnant woman; a two-dimensional (2D) color map generator which generates a 2D color map based on the sample image; a probe which irradiates ultrasonic signals toward a fetus of the pregnant woman and receives reflected ultrasonic echo signals; a volume data generator which generates three-dimensional (3D) volume data based on the ultrasonic echo signals; and a controller which generates a 3D ultrasonic color image of the fetus by applying values of the 2D color map to a 3D ultrasonic image obtained by volume rendering of the 3D volume data.