1. An apparatus for generating an ultrasonic image, the apparatus comprising: a sample image acquisition unit configured to acquire a sample image by photographing a portion of a skin of a pregnant woman; a probe configured to irradiate ultrasonic signals toward a fetus of the pregnant woman and receives reflected ultrasonic echo signals; a processor configured to generate a 2D color map based on the sample image, generate three-dimensional (3D) volume data based on the ultrasonic echo signals, and generate 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.