To correct this, you must open the artwork in the graphic program that created it and change the color name to match that used in the layout program. It is possible that the type of graphic file may be to blame. United Graphics, Inc. discourages the use of clip art for this reason. And don't forget to convert any RGB graphics to CMYK for four-color printing. Or if your artwork is to print black, be sure to convert to greyscale.
Some programs default to always overprint black.
Designers should be aware that this is not always appropriate. It is OK to overprint black if it is over continuous tone. If black is placed over multiple colors, such as a 4-color separation or blocks of color, it cannot overprint. If it does, the colors beneath will show through, creating multiple shades of black. You will not be able to see this problem printing to a color printer.