RGB vs. CMYK - What is the difference?

RGB (Red/Green/Blue) is the color space for electronic devices. Everything you use that is digital uses the RGB color space. Colors are made with light.

CMYK (Cyan/Magenta/Yellow/Black) is the color space used for print. The colors are created using cyan, magenta yellow and black inks and are applied to the surface (often paper) with printing plates (usually metal). For a full-color print using this technology, 4 plates are used. Ink is applied in sequence with black being printed last (on top).

Why should you care?

If someone submits an RGB file for a printing job, it will be converted to a CMYK file. A press cannot print directly from an RGB file. When the conversion is done, shifts in color occur. Those shifts can be downright ugly since there are many colors that look great onscreen but are uber-ugly when converted to CMYK. Doing the conversion yourself, then adjusting the color, will ensure you get what you want when printing.

To utilize a CMYK file in a website, it will first have to be converted to RGB. A CMYK file will usually produce an error message if an attempt is made to upload it without first converting.