An image generating apparatus and program capable of realistically displaying an image of a submerged land portion in consideration of water characteristics is provided. In rendering processing, when an object to be rendered is a water surface object, from color data (VR, VG, VB) of an object such as a land already written in the frame buffer, new color data (VR′, VG′, VB′) is generated according to color parameters (&agr;r, &agr;g, &agr;b) predetermined based on the water characteristics. The color parameters are so determined that the ratio of reducing a red color component value VR becomes larger than the ratios of reducing a green color component value VG and a blue color component value VB (&agr;r