A color image forming apparatus comprising: an input device for inputting image signals denoting a plurality of color components; an under color processing device for processing the under colors of the image signals denoting a plurality of the color components supplied by the input device; an image forming device for forming images in response to the image signals denoting a plurality of the color components, which have been processed by the under color processing device, and image signals denoting the under colors by using coloring agents which correspond to a plurality of the color components and the under colors, the coloring agents, which correspond to the under colors, having glossiness lower than that of the coloring agents which correspond to a plurality of the color components; and a control device for controlling the glossiness of the image formed by the image forming device by controlling the quantity of process of the under colors processed by the under color processing device.