Why "K" and not "B"? Colour mysteries revealed.

June 11, 2015

In Design-land we tend to throw around colour-related jargon like a frisbee at the beach. But how much do we really understand what the terms mean, and how we are best to apply them to our everyday projects?

Let's strip away some of the more popular acronyms and terminology.

Web colours:


RGB stands for "red, green, blue" - the system for specifying all colours used on a computer display or TV screen. Red, green and blue can be combined - in various proportions - to obtain any colour in the visible spectrum.

Levels of R, G and B can range from 0% to 100% of full intensity, and this level is represented by a range of numbers from 0 to 255 (256 levels for each colour).

When you see RGB numbers specified it will look similar to this: 238/18/137 (deep pink), showing red, green and blue values respectively. You always specify the numbers in the order of R, G, then B.


A hex (hexadecimal) number is the six-digit set of letters and numbers used in web projects (HTML, CSS, SVG), usually preceded by a #. You may come across this in CMS systems where you have to specify colours for fonts and backgrounds.

The digits represent the red (first two digits), green (middle two digits) and blue (last two digits) components of every screen-based colour.

Hex numbers will be made up of the following numbers and letters: 0 1 2 3 4 5 6 7 8 9 A B C D E F. Zero is the smallest amount of colour (often the absence of colour), and F is 15 times the intensity of the colour of 0. Double zero (00) is equal to zero hue. FF is equal to a pure colour. FFFFFF is white (the combination of red, green and blue on a computer screen equals white), and 000000 (a total absence of colour on a computer screen) is black. You'll notice that this is the direct opposite - in terms of colour theory - to printed colour.

Print colours

CMYK and 4-colour

CMYK refers to the four inks used in a standard "4-colour" printing process (cyan, magenta, yellow and black). Depending on the printing company or the press used, the inks are usually applied to the paper (or substrate) in the same order as per the CMYK abbreviation

The "K" in CMYK refers to "key". In 4-colour printing the black "key plate" is used to carefully align the other three colour plates, so that all the elements are in perfect registration. A popular notion is that if "B" was used to denote "black" it might be misconstrued as "blue", which was already taken by cyan. This is a handy explanation, but is technically and historically incorrect.

You may hear some of the older design fraternity referring to a thin black outline (such as around a photograph or a print ad) as a "keyline". Back in the "old" days (prior to using computers), a black keyline was used to show photolithographers where block colour boxes, ads and photographs were to appear in a page layout.


My sincere wish was that Pantone had chosen a different acronym for their world-famous colour system other than "PMS" [sigh, alas not]. Used since the 1950s, PMS (Pantone Matching System) colours are an industry standard worldwide. 

The Pantone system comprises of thousands of colour swatches, each with its own unique number. By standardising these colours and numbers, different ink manufacturers, printers and designers can all specify the same number to ensure a colour match - no matter where in the world they are located.

Example: Pantone 199, a dark red, is specified as "Pantone (or PMS) 199C" (C for coated paper; "M" for matte paper; "U" for uncoated paper). The ink breakdown (for printers) is 12 parts Pantone Rubine Red and 4 parts Pantone Yellow. The CMYK breakdown (for designers) is 0/100/65/0.

Spot and special colours

"Spot colour" and "special colour" are synonymous offset printing terms. They refer to any colour of ink that is printed using a single run on the printing press.

Companies will often print using a spot colour to maintain brand consistency. For example, Cadbury prints all of their chocolate packaging and promotional material with a purple spot colour. This ensures that the Cadbury purple is the same no matter which printer or printing press generates the work.

It's nigh on impossible to closely match a spot colour with a CMYK breakdown (especially for oranges and blues). If colour-match is critical then printing spot colour is the only way to go. Spot colours are also more intense and vibrant than a similar colour made out of CMYK inks.

Full colour

Often the terms "full colour" and "4-colour" are interchanged as if they mean the same thing. Most often times they do, but you have to be careful.

"4-colour" specifically refers to the CMYK printing process (as detailed above). "Full colour", on the other hand, simply refers to a printed piece that is in colour (as opposed to black and white or a simple one or two-spot colour job). "Full colour" could also mean a piece that is printed CMYK + other spot colours (e.g. a 5, 6 or 7-colour job). It pays to use the correct term in order to eliminate potential confusion.

Rich black

Rich black, in printing, is an ink mixture of solid black plus one or more of the other CMYK colours, resulting in a darker tone of black. 100% black is rather insipid and can look somewhat grey. A rich black gives you a true "black black".

The actual CMYK breakdown of rich black varies wildly (there is no right or wrong), but typical mixes could be:
50/50/50/100 - a standard mix
70/35/40/100 - a cool black
35/60/60/100 - a warm black

Use of rich black can be for either aesthetic or technical reasons. You'd need to use rich black for the following print situations:

  • When printing black on a backlit (translite) substrate, to ensure the black actually looks "black" and blocks out the light.
  • When a block of black overlaps another colour or an image. If you used 100% K only, you would see the base image or colour showing through. Rich black blocks this base image out.

Be careful with the percentages of CMYK used in making rich black. Some publications have a "maximum ink coverage" percentage for submitted artwork. A safe rule-of-thumb is that total ink coverage (e.g. C% + M% + Y% + K%) should not exceed 240% on normal papers...or else the ink becomes too wet and cannot dry in time.

Is white a printing colour?

Yes, absolutely you can print white with offset printing. White is considered a spot colour (the same as any other Pantone colour).

Talk with your printer if you think you will want to print with white ink. Depending on the paper stock and type of ink, you may need two "hits" (or passes) of white to make the white solid enough. In the case of a double pass being required, white would be considered as two additional spot colours (as it's double the ink, double the costs, etc).

Laser or inkjet printers cannot print white as - in this case - white is made up of 0C/0M/0Y/0K, which equals zero ink for machines with only CMYK cartridges. Some digital printing presses now have a white toner cartridge, in which case printing with white becomes an option.

Colour theory

Unless you are a designer you won't need to know in-depth colour theory to get by. It does help, however, to have a top-level understanding of the various colour spaces and terminology that exist in our industry. Not only will the knowledge help you in your day-to-day tasks, but it will make you sound a whole lot smarter during your client and team conversations...and who doesn't want that?!


If you have more colour tips, let us know in the comments below!



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