1. A color gamut data creating device comprising: a receiving unit configured to receive measurement points concerning a device, the measurement points being defined in a color space that is capable of representing hue by a hue angle, the hue angle being defined by an axis perpendicular to an achromatic axis that represents lightness; a projecting unit configured to project the measurement points on a projecting plane that is perpendicular to the achromatic axis; a first vertex determining unit configured to determine a vertex of a polygon that is formed based on the measurement points projected onto the projecting plane; a vertex angle determining unit configured to determine a hue angle of the vertex; a target-plane angle determining unit configured to determine a hue angle of a target plane based on the hue angle of the vertex determined by the vertex angle determining unit, the target plane being perpendicular to the projecting plane; a locating unit configured to locate hull points on the target plane based on the measurement points projected onto the projecting plane; and a data creating unit configured to create color gamut data indicative of a color gamut indicative of a distribution range of the measurement points based on the hull points on the target plane.