Choosing colours for brands, reports and charts

Colour is often the first thing people notice about a report, a slide deck or a chart. It signals who the document comes from, what to look at first and how values relate to each other. It is also where many publications quietly fail: pale text that cannot be read on a phone in sunlight, or a chart whose lines look identical to some readers.

Good colour choices are not about personal taste. They follow a few clear rules on brand consistency, contrast and data. This guide covers all three, so that your brand colours, your report layouts and your colour palette for charts work together.

Most organisations have one or two brand colours, often chosen for a logo. A logo alone is not a palette. Before anyone designs a report, extend your brand colours into a small system that people can use every day.

In our own practice, a useful brand palette usually includes the following. Record each colour in the formats your team needs, such as HEX for screens and CMYK for print, and note which combinations are approved for text.

• One or two primary brand colours for headings, covers and key highlights.
• Two or three supporting colours that work with the primary colours in charts.
• A dark neutral for body text and a range of greys for backgrounds, lines and labels.
• Lighter tints of each colour for panels, tables and sequential chart scales.
• Clear rules on which colour pairs may be used for text, and which may not.

Contrast is the difference in lightness between text and its background, measured as a ratio. The Web Content Accessibility Guidelines (WCAG) require text to have a contrast ratio of at least 4.5:1, and large text a ratio of at least 3:1.¹ Large text means at least 18 point, or 14 point bold.¹ The guidelines set no contrast requirement for text that is part of a logo or brand name, but that exception does not cover the rest of your materials.¹

This matters for brand colours. Many bright brand colours, such as yellow, orange or light green, fall well short of 4.5:1 against white. Use them for large shapes, borders and highlights, and set body text in a dark neutral. Free contrast checkers let you test any pair of colours in seconds, so build the check into every new template.

Contrast applies beyond text. WCAG asks that the parts of graphics needed to understand the content have a contrast ratio of at least 3:1 against adjacent colours.² In a line chart, each line should reach 3:1 against the background.²

The right colour palette for charts depends on the kind of data. Datawrapper's guidance describes three types of colour scale.³ Categorical scales use different hues, such as blue, orange and green, to tell apart categories that have no natural order.³ Sequential scales run from light to dark and suit numbers that go from low to high, such as income or age.³ Diverging scales have a light middle value and grow darker towards each end in different hues, which suits negative and positive values or survey answers on an agree to disagree scale.³

Fewer colours make a chart clearer. The UK Government Analysis Function notes that limiting the number of colours in a chart makes them stand out, and recommends a limit of four categories as best practice for basic charts.⁴ For sequential data, it advises a single hue or a small set of closely related hues, changing lightness rather than switching between unrelated colours.⁴

Use grey to support the data. The same guidance recommends grey for axes and labels, and describes focus charts that show one series in a strong colour and the rest in light grey.⁴ This is often the simplest way to use a brand colour in a chart: give it to the one bar or line you want readers to notice.

Some of your readers see colour differently. Datawrapper cites estimates that about 8% of European men and 0.5% of European women have some kind of red or green colour weakness or colour blindness, while cautioning that such figures are uncertain.⁵ People with red or green colour blindness can struggle to tell red, green and brown apart when the colours have the same brightness.⁵

The most reliable fix is to vary lightness as well as hue. Datawrapper recommends giving categorical colours different lightnesses so that they also work in greyscale, which helps colour-blind readers in particular.³ The Government Analysis Function says it checked its suggested palettes for different types of colour blindness and in greyscale.⁴ Printing a chart in black and white, or viewing it in greyscale on screen, is a quick test any team can do.

Be careful with red, amber and green status ratings. The Government Analysis Function found that it is not possible to choose red, amber and green shades that have enough contrast with a white background and with each other, and suggests adding text labels instead of relying on colour.⁴

WCAG states that colour must not be the only visual means of conveying information.⁶ Its examples include a chart where one person's sales are shown in red and another's in blue: readers who cannot tell the colours apart lose the meaning.⁶ The guidance lists using colour together with pattern as one way to meet the rule.⁶

In practice, label lines and bars directly instead of relying on a legend, add values or symbols where they help, and use patterns or texture in print. The Government Analysis Function recommends labelling lines directly and providing a plain text alternative for charts.⁴ For pie charts, WCAG gives an example where a darker border around a pale slice lets readers see where each slice ends.²

Colour decisions only help if people apply them. Write the palette, the approved text combinations and the chart colours into your brand guidelines, then build them into the tools people actually use: report templates, slide masters and the default colour settings in your charting software.

Give chart colours a fixed order, so that the same category keeps the same colour across a report. The Government Analysis Function recommends using its categorical palette in the listed order, starting with the first colour.⁴ Review new materials against the checklist below before they go to print or online, and update the palette when you find a combination that does not work.

• Brand colours extended into a small palette with neutrals and tints
• Body text at 4.5:1 contrast or more against its background
• Chart lines, bars and slices at 3:1 or more against adjacent colours
• Scale type matched to the data: categorical, sequential or diverging
• No more than four colours in a basic chart, with grey for context
• Palette checked in greyscale and for colour blindness
• Direct labels, values or patterns so colour is never the only cue
• Palette built into report, slide and chart templates