Short answer
Four things together: a text alternative that conveys the chart's point and, for complex charts, its data (1.1.1); colour that is never the only way to tell series apart (1.4.1); 3:1 contrast for the lines, bars and markers needed to read it, unless labels or values carry the same information (1.4.11); and 4.5:1 for axis labels, legends and annotations (1.4.3). Interactive charts must also be operable by keyboard with visible focus.
A chart is an image of data, so its first accessibility requirement is the one every meaningful image has: a text alternative. The W3C's tutorial on complex images recommends two parts — a short alternative that identifies the chart and says where the full description is, and a long description that conveys the essential information, which for data-heavy charts can include a table of the values. Write the short alternative as the chart's point ('Sales doubled between 2020 and 2024, driven by online orders'), not its type ('Bar chart'). The long description and data table serve screen-reader users, but also anyone who cannot distinguish the colours, anyone using a magnifier who sees only part of the chart, and anyone who wants exact figures.
Two colour criteria apply to the graphic itself. Under 1.4.1, series or categories identified only by colour fail; a legend of coloured swatches does not help someone who cannot tell the colours apart, so series need direct labels, distinct markers or patterns. Under 1.4.11, the parts of a graphic required to understand it — bar fills, line strokes, markers, map region boundaries — need 3:1 against adjacent colours. The Understanding document makes an important exception: if the chart shows the information in visible text as well, such as data labels on every bar or values on a pie segment, the graphical parts themselves do not need to reach 3:1. That makes labelling the most powerful single fix, since it satisfies 1.4.1 and relaxes 1.4.11 at once.
Choropleth maps encode values in colour by design, which puts them in tension with 1.4.1. Adjacent regions often need only to be distinguished by their borders, which should be clearly visible, while the value of each region must be available in another way: a hover or focus tooltip, labelled values for key regions, or a linked table. Point maps with coloured markers should vary marker shape as well as colour. Map tiles and basemaps usually carry low-contrast roads and labels; where the map is the content rather than decoration, check that the features users need stand out. And a map that works only by pointer hover fails keyboard users unless the same information can be reached by tabbing or from a table.
Interactive charts add keyboard requirements. Every tooltip, filter and data point that a mouse user can reach must be reachable by keyboard, with a visible focus indicator on the focused element and focus that is not hidden behind other layers. Tooltips triggered by hover or focus should be dismissible and should stay visible while the pointer moves over them. Highlighting a series on hover by dimming the others is a helpful visual device, but the dimmed series should still be readable if they are needed. Animated transitions should respect the reduced-motion preference. The palette side of chart design — choosing colours that survive colour-vision deficiency, greyscale and dark mode — is covered in the data-visualisation pillar.
| Part of the chart | Criterion | What it asks | Usual fix |
|---|---|---|---|
| The chart as a whole | 1.1.1 Non-text Content (A) | A text alternative serving the same purpose | Short alt stating the point, plus a long description or data table |
| Series and categories | 1.4.1 Use of Color (A) | Not distinguished by colour alone | Direct labels, marker shapes, patterns |
| Bars, lines, markers, region borders | 1.4.11 Non-text Contrast (AA) | 3:1 against adjacent colours where needed to understand | Darker marks, or visible data labels |
| Axis labels, legends, annotations | 1.4.3 Contrast (Minimum) (AA) | 4.5:1 (3:1 for large text) | Darker text greys |
| Tooltips, filters, data points | 2.1.1 Keyboard (A); 2.4.7 Focus Visible (AA) | Operable by keyboard with visible focus | Focusable points or a linked table |
Why: The alternative text names the chart type, not its message.
Fix: State the chart's main finding in the alternative and link a data table.
Why: Series are identified only by colour.
Fix: Label lines directly or vary markers.
Why: Tooltips are not reachable by keyboard.
Fix: Make regions focusable or provide a sortable table.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
ConventionStrong evidence
The W3C's complex-images tutorial recommends giving charts, graphs and maps a short text alternative plus a long description of the essential information, which may include a data table.
Source: Complex Images (Images Tutorial)
StandardStrong evidence
Under WCAG 1.4.11, parts of a chart need 3:1 against adjacent colours only where they are required to understand the content; if the same information is provided in visible text such as labels and values, the graphical parts need not meet 3:1.
Source: Understanding Success Criterion 1.4.11: Non-text Contrast (WCAG 2.2); Web Content Accessibility Guidelines (WCAG) 2.2
StandardStrong evidence
The W3C's Understanding document for 1.4.1 gives a diagram whose elements are identified by colour and by numbers as an example of meeting the criterion, since the numbers work for people who cannot distinguish the colours.
Source: Understanding Success Criterion 1.4.1: Use of Color (WCAG 2.2)
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.