1. A color conversion device, comprising: a control unit configured to execute a color conversion program stored on a non-transitory computer-readable recording medium, the control unit comprising: a hue acquisition unit that acquires a hue of a plurality of second target colors, each second target color having an approximately same lightness and an approximately same chroma as a first target color within each of one or more Voronoi diagrams, wherein each generation point of each Voronoi diagram corresponds to one of a plurality of predefined colors included in a color conversion table, wherein the color conversion table defines a correspondence between a plurality of colors in a first color system and a plurality of colors in a second color system, wherein each Voronoi diagram corresponds to a plurality of groups into which a plurality of predefined colors are classified according to respective ranges of a series of hues; a side group acquisition unit that acquires two side groups based on a hue of the first target color and the hue of the second target color, wherein each side group is included in the plurality of groups and is located on either side of the first target color in terms of the hue; and a color conversion unit that acquires a third target color by converting the first target color to a color in the second color system based on the predefined colors corresponding to the side groups and the first target color.