A color image data processing apparatus processes hue information of picture elements read out sequentially. A chromatic color detection unit is provided for detecting a chromatic color picture element series in a main scanning line having a consecutive succession of chromatic color picture elements including edge picture elements. A replacing unit is provided for replacing the hue value of each picture element of the chromatic color picture element series with a median hue value, the hue value of a picture element located approximately at the center position of the detected chromatic color picture element series. The apparatus may further have an averaged hue value switching unit for switching the hue value of each of the picture elements with an average of the hue value of the picture elements and of other picture elements located in a nearby region.