Working with Colour Models

The colour name system

Simply typing a colour name – such ‘red’ or ‘blue’ (without quotes) – in a CSS style rule is a common starting point when designing a new web page.

h1 { color: red }

Many colour names are both easy-to-remember and self-explanatory. For example, ‘yellow’, ‘purple’ and so on. Other colour names are less obvious, such as ‘hotpink’, ‘mediumvioletred’ and ‘lavenderblush’.

Colour names are not case-sensitive. For example, these three versions of the same colour name are all valid.

h3 { color: DarkOrchid }
h3 { color: darkorchid }
h3 { color: DARKORCHID }

You can see a full list of colour names on this W3 Schools web page.

However, the final version of a web page will typically use either RGB values or hex codes rather colour names for the following two reasons:

• Limited choice: Modern electronic screens can display at least 16 million different colours. With colour names, you are limited to only 147 choices.
• Misleading names: Even when colour names are easy-to-remember, they are not always accurate. For example, DarkGray is actually lighter than Gray.

Note that, in CSS, the colour name of grey can be written in either US spelling (gray) or UK spelling (grey). Either will work correctly.

The RGB colour system

The RGB system is based on the following idea:

Any colour can be created by combining different intensities of the three primary colours: red, green and blue.

Here are a few points about the Red-Green-Blue colour system:

• Every RGB colour is written as a list of three values: first the red value, then the green value, and then the value for blue. The individual values are separated from one another by commas.
• You can write each individual value as a number in the range 0 to 255. The following RGB code will produce the colour red:   255,0,0
• The three values are enclosed within brackets and preceded by the letters rgb (in lower-case or upper-case). In the example of red, the CSS value would look as follows:   rgb(255,0,0)

The following examples of CSS style rules show the RGB system used to create the three colours of blue, a light brown and magenta.

h1 { color: rgb(0,0,255) /* blue */ }
h2 { color: rgb(255,248,220) /* light brown */ }
h3 { color: rgb(255,0,255) /* magenta */  }

The hex code colour system

This is the colour system most widely used in web design. As with the RGB system, the displayed colour is created by combining different intensities of red, green and blue. But the hex (short for hexadecimal) code system is different in four ways:

• The hex colour code begins with the hash (#) symbol.
• No commas are used to separate the red, green and blue values from one another.
• The list of red, green and blue values is not enclosed in brackets.
• The red, green and blue values are each written as a pair of two hexadecimal numbers.

Here are the three colours of blue, light brown and magenta written as hex codes in CSS style rules.

h1 { color: #0000FF /* blue */ }
h2 { color: #FFF5DC /* light brown */ }
h3 { color: #FF00FF /* magenta */ }

Like colour names, hex codes are not case-sensitive. For example, both #0000ff and #0000FF are valid and display the colour blue.

Decoding the hex colour system

A hex colour code may look like a random jumble of numbers and letters. Given that this system is so widely used in web design, however, it is worth taking a few moments to understand how this colour system works.

Here are the main points to note:

• In the everyday decimal system, there are 10 number symbols: 0, 1, 2, 3, 5, 6, 7, 8 and 9.   In the hexadecimal system, however, there are 16 number symbols: 0, 1, 2, 3, 5, 6, 7, 8, 9, A, B, C, D, E and F.
• The hexadecimal numbers A, B, C, D, and E are equal to the decimal numbers 10, 11, 12, 13, 14 and 15.
• Every hex colour code is really a combination of three number pairs.
• As in the RGB system, the first pair is the red value, the second pair is green and the third is blue.
• The smallest possible value for a pair of two hex numbers is 00. This hex code pair is equivalent to a zero decimal percentage (0%) or the decimal number zero (0).
• The largest possible value for a pair of two hex numbers is FF. This hex code pair is equivalent to one hundred per cent (100%) in decimal or the decimal number of 255.

So, in the hex colour code system:

• The colour white is #ffffff, as all three primary colours are at their maximum intensity: rgb(255,255,255).
• The colour black is #000000, as all three primary colours are set to zero: rgb(0,0,0).

Three-character, short-hand hex codes

Not every hex colour code needs to be written as a string of six digits. You write some hex colours in three-digit shorthand.

Consider the example of the colour white. In CSS, you can write this in two ways:

#ffffff

-or-

#fff

The general rule is as follows:

If any one of the three pairs in a six-digit hex code is a duplicate, you need only write that hex digit once.

You can see some more examples of three-digit hex codes below.

For every colour above, three pairs of duplicate hex digits (such as 00, 33 or FF) are shortened into one digit.

Colour contrast and accessibility

Some colour combinations that are easy for most people to read are difficult or impossible for others. It is estimated that about 20% of web users have some form of limited vision.

In particular, about 1 in 12 men and 1 in 200 women have some form of 'colour blindness'. That means about 5% of your website visitors will not experience your site the way you intended.

There is little point in creating great text content for your website if a significant percentage of your website visitors struggle or cannot read what is on their screens.

An important factor is colour contrast – the difference between the foreground and background colours.

The WebAIM guidelines recommend a minimum contrast ratio of 4.5:1 for text on web pages. For headings and other large text, a contrast ratio of 3:1 is sufficient.

Notice the difference in the contrast ratios shown below. The image is from Google's web.dev website.

After you have chosen a colour palette, you are now ready to apply it to the website template.