Image forming apparatus for increase of color toner in a color toner image in a special operation

An image forming apparatus comprising:

• an image forming unit including:
• a color toner unit including a color toner developing device containing a color toner comprising at least one of yellow toner, magenta toner, and cyan toner, the color toner developing device configured to form a color toner image with the color toner on a recording medium;
• a replaceable black toner unit including a black toner developing device containing black toner, the black toner developing device configured to form a black toner image with the black toner on the recording medium;
• and
• a replaceable special toner unit including a special toner developing device containing a special toner, the special toner developing device configured to form a special toner image with the special toner on the recording medium;
• a unit holder configured to selectively and detachably hold the replaceable black toner unit or the replaceable special toner unit;
• and
• circuitry to control the image forming unit to:
• form a color-black image on the recording medium, including the color toner image and the black toner image, during a normal operation when the unit holder holds the replaceable black toner unit;
• and
• form a color-special image on the recording medium, including the color toner image and the special toner image, during a special operation when the unit holder holds the replaceable special toner unit;
• wherein an amount of the color toner per unit area, in the color toner image formed on the recording medium, is relatively increased during the special operation relative to the normal operation.