What is claimed is:1. A display device comprising:an obtainer that obtains information on at least one special color to be printed, the information being information on the at least one special color with respect to at least one basic color; anda display controller that:(1) performs control to display a portion where the at least one special color is to be printed in accordance with a color value corresponding to a degree of transparency obtained from the information on the at least one special color, which is obtained by the obtainer, and(2) adjusts the degree of transparency for the at least one special color to be lower when the at least one special color is to be printed behind the at least one basic color than when the at least one special color is to be printed in front of the at least one basic color.2. The display device according to claim 1, wherein the obtainer obtains a density of the at least one special color.3. The display device according to claim 1, wherein the display controller adjusts the degree of transparency for the at least one special color to be higher when the at least one special color is to be printed in front of the at least one basic color than when the at least one special color is to be printed behind the at least one basic color.4. The display device according to claim 1, wherein the display controller adjusts the degree of transparency for the at least one special color in accordance with color information of the at least one special color.5. The display device according to claim 1, wherein the display controller includesa basic color converter that converts color data of the at least one basic color into RGB data,a special color converter that converts data of the at least one special color into RGB data, anda combiner that combines the RGB data of the at least one basic color, which is obtained by the basic color converter, with the RGB data of the at least one special color, which is obtained by the special color converter, by using the degree of transparency for the at least one special color.6. The display device according to claim 1, wherein the display controller adjusts the degree of transparency for the at least one special color in accordance with information on an arrangement of the at least one special color with respect to the at least one basic color.7. A printing system comprising:a printer that prints an image on a recording medium; anda display device that displays an image to be printed by the printer,the display device includingan obtainer that obtains information on at least one special color to be printed, the information being information on the at least one special color with respect to at least one basic color, anda display controller that:(1) performs control to display a portion where the at least one special color is to be printed in accordance with a color value corresponding to a degree of transparency obtained from the information on the at least one special color, which is obtained by the obtainer, and(2) adjusts the degree of transparency for the at least one special color to be lower when the at least one special color is to be printed behind the at least one basic color than when the at least one special color is to be printed in front of the at least one basic color.8. A non-transitory computer readable medium storing a program causing a computer to execute a process for display, the process comprising:obtaining information on at least one special color to be printed, the information being information on the at least one special color with respect to at least one basic color;performing control to display a portion where the at least one special color is to be printed in accordance with a color value corresponding to a degree of transparency obtained from the obtained information on the at least one special color; andadjusting the degree of transparency for the at least one special color to be lower when the at least one special color is to be printed behind the at least one basic color than when the at least one special color is to be printed in front of the at least one basic color.