1. An image forming device comprising: an image forming unit that forms an image onto a recording medium, the image comprising at least one of a test image and a user-requested image; a controller that controls the image forming unit to form a test image including a mixed color on the recording medium; a transporting path that transports the recording medium on which the test image is formed by the image forming unit; an image detecting unit disposed at the transporting path that detects the test image formed on the recording medium; and a calibration unit that performs a color calibration process based upon the test image detected by the image detecting unit.