OK first up, colours displayed on screen are in RGB mode, colours in printed material are in CMYK or ‘spot’ colours (see definitions below). What this means is you can’t really expect to hold up a printed document next to screen and expect them to match perfectly. It is possible on a colour calibrated screen and a colour calibrated printer outputting to specific paper to get a pretty close match, but generally in an office environment you won’t have either of these so you will get variation. Variables such as the brightness, age, quality and even the light conditions in the room play a part in mis-matching. Different papers - coated or uncoated have a significant effect on colour in printed materials, so when looking at colour consistency, always judge with these variables in mind.
Colour gamut is the term that refers to the range of colours possible on a device such as a computer screen or printer. RGB (screen) generally has a wider colour gamut than a printer which uses CMYK. High-end screen monitors have a ‘wide colour gamut’. The latest iPhones for instance and OLED 4K TVs have an extremely wide colour gamuts — the colours you see are a true representation of the colour intended. In comparison older computer monitors and LED screen have smaller gamuts and can't display all the colour information in the media they are showing. Also an uncalibrated screen is often prone to colour casts.
They way we see colour also changes in different light conditions. For example a printed item will look dramatically different in daylight to interior lighting. We actually see colours in RGB - the combination of reds, greens and blues. An individuals perception of colour relies on the combination of these being interpreted correctly by the brain (remember the Gold or blue dress meme?). In the UK, around 10% of males and 8% of females have genetic deficiencies (commonly known as colour blindness) that vary in severity depending on which of the colour areas are compromised.
Some definitions and dos and dont's:
CMYK is the colour mode used for printing. Colours will be separated out into 4 inks/colours: cyan, magenta, yellow and black. Commonly known as ‘Four colour printing’ or ‘Four colour process’ or even just ‘process’.
RGB is the mode used by screens to reproduce colour. Colours are created by the combination of red, green and blue light. With OLED screens the actual pixels produced their own light which gives them excellent colour rendering ability, LED screens are backlit to illuminate the pixels so are less accurate than OLED.
Spot colours are special inks formulated to a particular single colour (much like paints). The Pantone Matching System (PMS) is the most widely used spot colour system.
Do make sure images or logos intended to be used on screen are in RGB colour mode, and images or logos to be printed, are in CMYK.
Remember copying files from one software application to another can alter the colour information.
Don’t judge colours on an older uncalibrated screen.
When judging a printed piece for colour try to view it in daylight rather than artificial light, although strong sunlight should be avoided.
Coated papers offer better colour reproduction than uncoated (but you might want the effect of an uncoated paper but don’t expect good colour consistency).
Don’t judge colours printed on your office printer. Your office desktop printer can produce accurate colours (if its set up correctly), but most the time, lets face it, it probably won’t. Again the paper you print on, the set-up and quality of the device will cause huge variation.
For consistency of a single colour in print, do use a ‘spot’ colour rather than CMYK. It is often more expensive to use spot colours, but if accuracy and consistency is needed it might be worth considering.