Everything that you see on your computer screen is created out of the colours Red, Green and Blue – RGB. They work together to create bright, vibrant and vivid colours. Full colour printing uses Cyan, Magenta, Yellow and Black – CMYK – to create more colours, contrasts, tones and half-tones.
If you are sending an artwork file created in Publisher, Photoshop or one of the common graphics packages you need to change your artwork from RGB to CMYK.