1. A control device comprising: a control unit that controls generation of information for forming a first transparent image on the basis of settings that include at least a superimposition region and a superimposition sequence, the superimposition region being a region where a first color image, a second color image and the first transparent image are superimposed, and the superimposition sequence defining a sequence of superimposition of the first color image, the second color image and the first transparent image; wherein the settings further include a density of the first transparent image and a density of a second transparent image, the control unit generates the information for forming the first transparent image on the basis of the settings, the control unit controls generation of information for forming the second transparent image on the basis of the settings, and when, on the basis of the superimposition sequence, the first transparent image is to be superimposed on the first color image and the second transparent image is to be superimposed on the second color image, the control unit (i) synthesizes the first transparent image and synthesizes the second transparent image by adding the density of the first transparent image and the density of the second transparent image at each pixel thereof within the superimposition region, and (ii) generates the information for forming the first transparent image and generates the information for forming the second transparent image.