We get asked this time to time – 4/0 refers to full colour printing on one side of the printed page. 4/1 refers to full colour printing on one side and black printing on the other side. 4/4 refers to full colour printing on both sides. If you want just one colour (beside black ) on the sheet when one side is full colour, the one colour is made up of CMYK and it would be a 4/4 printed product even though it looks like one colour. CMYK is the abbreviation for Cyan, Magenta, Yellow, and Key (Black). This is the industry standard process colours used in full colour offset printing. The combination of these four colours can produce a wide array of colours.. 4/0/, 4/1 or 4/4 can also mean the same thing for spot colours. Always ask your designer or printer if in any doubt as mistakes or misunderstanding in print can be costly and unnecessary.