1. A method for processing of color information of a document provided with noise characters and usable characters, the method performed by a computer system with a processor and memory, the method comprising the steps of: generating a digital image of the document comprised of image points whose color is respectively established by a brightness value, a saturation value, and a color tone value; selecting at least one image region of a first type which is known to correspond to a region of the document that contains noise characters but no usable characters; establishing a brightness value range based on brightness value ranges of image points of the image region of the first type, said brightness value range being assumed to contain brightness values of the image points corresponding to the noise characters, wherein establishing the brightness value range is performed by the processor executing instructions stored in the memory; for saturation values of those image points of the image region of the first type whose brightness values lie in the established brightness value range, respectively determining a frequency with which these saturation values occur in the image region of the first type, wherein determining the frequency with which these saturation values occur is performed by the processor executing instructions stored in the memory; based on those saturation values whose determined frequency exceeds a predetermined value, establishing a saturation value range containing these saturation values, wherein establishing the saturation value range is performed by the processor executing instructions stored in the memory; for color tone values of those image points of the image region of the first type whose brightness values lie in the established brightness value range, respectively determining a frequency with which these color tone values occur in the image region of the first type, wherein determining the frequency of color tone values is performed by the processor executing instructions stored in the memory; based on those color tone values whose determined frequency exceeds a predetermined value, establishing a color tone value range containing these color tone values, wherein establishing the color tone value range is performed by the processor executing instructions stored in the memory; associating the colors of those image points of the image region of the first type whose brightness values lie in the established brightness value range, whose saturation values lie in the established saturation value range, and whose color tone values lie in the established color tone value range with a first color class of colors corresponding to the noise characters, wherein associating the colors with the first color class is performed by the processor executing instructions stored in the memory; associating the colors of those image points of the image region of the first type that are not associated with the first color class with a second color class of colors corresponding to a character-less document, wherein associating the colors with the second color class is performed by the processor executing instructions stored in the memory; selecting at least one image region of a second type which is known to correspond to a region of the document that contains neither noise characters nor usable characters; and excluding the colors of those image points of the image region of the second type whose brightness values lie in the established brightness value range, whose saturation values lie in the established saturation value range, and whose color tone values lie in the established color tone value range from the first color class and associating said colors with the second color class, wherein excluding the colors from the first color class and associating said colors with the second color class is performed by the processor executing instructions stored in the memory.