RGB (Red, Green, Blue) is a color model commonly used for computer and television display. For example, .jpg and .gif file formats use RGB color model.
Color model useable for printing is CMYK and the conversion between RGB and CMYK is ambiguous (there are different ways to do the conversion and they produce different results).
If you submit your artwork in RGB we will have to convert it to CMYK and submit the new version for your approval.
- Wikipedia in-depth article on RGB: http://en.wikipedia.org/wiki/RGB_color_model