Color image forming apparatus, and program and method of controlling a color image forming apparatus

An image forming apparatus comprising:

• a plurality of image forming stations, each image forming station configured to form a color toner image, the color of the color toner images being different among the plurality of image forming stations;
• first transferring parts and a second image carrying medium, the first transferring part configured to sequentially transfer the color toner images formed by the respective image forming stations to the second image carrying medium;
• a second transferring part adapted to transfer, in a second transfer process, the color toner images on the second image carrying medium to a recording medium;
• and
• a controller adapted to selectively switch a color mode between a full color mode, in which a full color image using plural color toner images formed on the second image carrying medium, and a single color mode, in which a single color image using a single color toner image formed on the second image carrying medium,
• wherein the controller controls the switching of the color mode by determining, based on an interval between an image of interest and an immediately previous image, whether there is an image of interest between a most downstream first transferring part and the second transferring part and whether it is possible to switch the color mode in a state in which the first transferring parts and the second-transferring part are not in operation,
• wherein responsive to the determination by the controller being affirmative, the controller switches the color mode after the second transferring process for the immediately previous image is completed and before the second transferring process for the image of interest is started, and
• wherein responsive to the determination by the controller being negative, the controller switches the color mode after the image of interest completely passes through the second transferring part.