1. A control device for controlling a printer comprising: a print head having a plurality of sets of nozzles, each of the plurality of sets of nozzles being configured to eject ink in one of a plurality of colors, the plurality of colors including a specific color and a plurality of different colors different from the specific color, the control device comprising: a controller configured to perform: acquiring target image data representing a target image, the target image including a first image within a first region and a second image within a second region; calculating an index value indicative of an amount of ink in the specific color to be used in printing at least a part of the target image; determining whether the index value is greater than a threshold value; in response to determining that the index value is not greater than the threshold value, controlling the printer to print the first image and the second image using the ink in the specific color but not using inks in the plurality of different colors for reproducing the specific color; and in response to determining that the index value is greater than the threshold value, controlling the printer to print the first image using the ink in the specific color but not using the inks in the plurality of different colors for reproducing the specific color and to print the second image using a combination of the inks in the plurality of different colors for reproducing the specific color.