CMYK stands for: Cyan, Magenta, Yellow & Black. They are the four process colors that represent the standard color mode for offset printing. Be sure when creating your print files to check that your color mode is set to CMYK. RGB is usually a default in raster based programs like photoshop. When working in RGB your colors will appear more vibrant. When converting a document from RGB to CMYK you may notice some shifting in color. Color shifts are usually not visible in color photographs; however, rich and solid colors (like a background) can be affected by a color conversion. Most of the time, color shifts are minor and may not be noticeable.