CYMK Vs RGB
So, you've read the Supplying Artwork page and are still non the wiser, here's a little more detail...
To achieve optimum colour reproduction, artwork should ideally be supplied in 'CMYK' colour mode as opposed to 'RGB'
'CMYK' is an abbreviation of Cyan, Magenta, Yellow and "Key" Black. These are the colours of the inks used for printing to achieve full colour images. 'RGB' is an abbreviation of Red, Green and Blue and these colours are what create the colour images on your computer monitor (and television)
By supplying artwork in 'CMYK' mode, no conversion from 'RGB' mode is necessary, therefore avoiding any colour shift from the original artwork. By converting 'RGB' artwork to 'CMYK' for output, colours can sometimes become flattened and less vibrant. 'RGB' mode is only necessary for artwork that is to be viewed on monitor (eg: websites / pages and email). By originating your artwork in 'CMYK' mode, you can rest assured that your printed article will give a more punchy effect and colours will be reproduced with absolute accuracy to the original artwork design.
Why use 3 colours (RGB) when you can use 4 (CMYK)...