Always use a combination of colour, shapes and text to convey meaning.

Always use a readable font, sentence case and a suitable font size – at least 12pt for web and print.

Why this matters...

Colour can be a simple and effective way to visually communicate meaning. What any given colour means, however, can vary from culture to culture. Furthermore, users that are colourblind or visually impaired will find it difficult to assess meaning if you rely on colour alone.
Shape is great for visual communication, but Individuals and cultures may interpret shapes differently. Furthermore, without alt text, shapes cannot be interpreted by screen readers. For this reason, shape cannot be used as the only way to communicate meaning.
Using font weight (bold) or size can be a great way to communicate meaning or emphasis. Text formatting, however, is not always identified by screenreaders, and so cannot be used as the only form of emphasis or meaning.
Design for inclusive communication

If you rely on colour, shape or text formatting as the only means of communication, you risk your message being misunderstood by some users. For example, a green button for good and a red button for bad may be generally understandable for most users. For someone colourblind, however, it may be indecipherable. In the word ‘good’ is used on the green button, and the word ‘bad’ on the red button, it encodes this information through multiple means. This increase both accessibility and inclusivity.

WebAim GuidanceMicrosoft Word