In the game space, n light sources for irradiating an object with a light beam are set. A brightness calculating section 521 and a texture coordinate generating section 522 obtain, for each of predetermined units forming the object, a brightness vector having as components n illumination intensities respectively added by the n light sources. A texture color determining section 523 determines, for each of the predetermined units, a region including a tip of the brightness vector from among regions obtained via division by threshold values based on relationships in size between the n illumination intensities and their corresponding threshold values. A display color determining section 524 determines a display color for each of the predetermined units based on the region determined for each of the predetermined units, such that the object's display color distinctly varies.