You’re probably aware that when it comes to computers, colours are represented by a series of numbers. In this post, John Espirian explains two of the most common colour systems used on the web.
There are lots of colour systems available, but the two mentioned here use the additive colour system. This means they are based on the combination of light, with the primary colours being red, green and blue. In the additive system, red, green and blue together produce white.
red + green + blue = white
For comparison, paints, dyes and inks use the subtractive colour system.
Sticking with the idea of light, imagine that the red, green and blue components are coloured torches pointing at the same spot. But these torches are special: instead of being either on or off, they can be partially on. Consider that the torches have analogue dials rather than on/off buttons.
With this idea in mind, we can move straight on to the two most popular colour systems on the web.
If you already know about RGB colours, take a look at this very useful resource for looking up colour values: rgb.to
Each of the RGB (red, green, blue) system’s three torches has a setting between
A value of
0 means the torch is off.
A value of
255 means the torch is on and shining at its maximum.
If all the torches are off, there’s no colour at all. This is black:
If all the torches are on and at their maximum, we instead see white:
To save space, we’ll use shorthand to represent some further examples:
RGB(0, 0, 0)is black
RGB(255, 0, 0)is red
RGB(0, 255, 0)is green
RGB(0, 0, 255)is blue
RGB(255, 255, 255)is white
To produce other colours, we just need to use different combinations of values. If you’re not used to additive colour, the results might sometimes seem a little counterintuitive. For example, yellow is red plus green:
RGB(255, 255, 0).
More RGB maths
red + green = yellow
A visual example should be helpful:
The above examples show our torches either off (
0) or on at maximum (
255). But any whole number in between these values is also valid. So we could have, say,
RGB(213, 82, 7), which has a large red value and smaller green and blue values. This colour looks orange.
HEX colours are exactly the same as RGB, but they’re expressed using hexadecimal (base 16) numbers instead of the decimal (base 10) system we’re more used to.
If you haven’t seen the hexadecimal system of counting before, it boils down to each column of numbers accepting more than 10 possible figures. Instead, we can represent up to 16 figures per column – and that’s done by using some letters as well as our usual numbers.
Here’s how this looks for the
16 numbers between
If we consider two-digit numbers, base 10 uses a ‘tens’ column and base 16 a ‘sixteens’ column. This means that RGB values can be expressed in fewer characters by using HEX. Here are some examples:
FF = (16 × 15) + 15 = 255
F0 = (16 × 15) + 0 = 240
AB = (16 × 10) + 11 = 171
86 = (16 × 8) + 6 = 134
Getting back to colours, we can represent the previous examples as follows:
Note that in HEX colour notation, we start the sequence of characters with the hash (#) symbol.
As you might be able to tell, the first two characters represent the red, the middle two characters the green, and the final two the blue.
An easy way to look up RGB and HEX colours
Keeping these conventions in mind isn’t always easy. Here’s an excellent resource for looking up RGB and HEX colours:
RGB and HEX colour website
https://rgb.to – look up RGB and HEX values
The website also includes details about Pantone and other colour systems.
If you click on any of the colour codes listed above, you’ll be taken to the relevant page on https://rgb.to – neat, eh?
Here’s another good colour resource:
Adobe Color CC (formerly Adobe Kuler)
https://color.adobe.com – a colour wheel for RGB and HEX
How many colours are there in the RGB and HEX systems?
Each torch’s value must be between
255, which means
256 possible values. We have
3 torches and must multiply the figures to work out how many possible colours there could be in these systems:
256 × 256 × 256 = 16,777,216
That’s more than 16.7 million colours.
Let’s wrap up
There’s a lot more that could be written about colour, but these basics should help you understand enough about two of the most popular colour systems used on the web.
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Who wrote this?
John Espirian – the relentlessly helpful technical copywriter
I write B2B web content, blogs, user guides and case studies – all aimed at explaining how your products, services and processes work. I also offer LinkedIn profile critiquing and rewriting.
I work from home in Newport, South Wales and support the (formerly) mighty Liverpool FC 🔴⚽️