Understanding Non-text Contrast

Intent

The intent of this Success Criterion is to ensure that active user interface components (i.e., controls) and meaningful graphics are distinguishable by people with moderately low vision. The requirements and rationale are similar to those for large text in 1.4.3 Contrast (Minimum).

Low contrast controls are more difficult to perceive, and may be completely missed by people with a visual impairment. Similarly, if a graphic is needed to understand the content or functionality of the webpage then it should be perceivable by people with low vision or other impairments without the need for contrast-enhancing assistive technology.

Active User Interface Components

For active controls on the page, such as buttons and form fields, any visual information provided that is necessary for a user to identify that a control exists and how to operate it must have sufficient contrast with the adjacent background. Also, the visual effects which are implemented to order to indicate state, such as whether a component is selected or focused, must also ensure that the information used to identify the control in that state has a minimum 3:1 contrast ratio.

Three buttons on a white background. The first has a dark grey border to indicate its boundary, white internal background and black text. The second adds a thick grey outer border to show focus. The third has the grey border with black background and white text.
An active control showing the visual boundary by default, the focus indicator, and the hover state.

This success criteria does not require that controls have a visual boundary indicating the hit area, but that if the visual boundary is the only way to identify that a control can be activated, then that boundary must have sufficient contrast. If text (or an icon) within a button is visible and there is no visual indication of the hit area, or the visual indication does not provide the only indication, then there is no contrast requirement beyond the text contrast (1.4.3 Contrast (Minimum)) or icon contrast covered by the Graphical Objects portion of this Success Criteria. Note that for people with cognitive disabilities it is recommended to delineate the boundary of controls to aid in the recognition of controls and therefore the completion of activities.

The visual focus indicator for a component must have sufficient contrast against the adjacent background when the component is focused, except where the appearance of the component is determined by the user agent and not modified by the author.

Two buttons, the first with no visual indicator except text saying 'button'. The second is the same but with an added grey border.
An active control without a visual boundary, but with a focus indicator when focused.

The Use of Color success criteria addresses changing only the color of an object (or text) without otherwise altering the object's form. If the states of an object vary by color this Success Criteria indicates that this is acceptable if the luminosity contrast ratio between the colors of the states differ by at least 3:1 or if there is another indicator of state. For example, a text link that only differs from adjacent text using color and there is no other visual indication that the text is linked (e.g. the link underline is removed) needs to ensure that the link color meets the 3:1 luminosity contrast ratio relative to the non-linked text color in order to meet this Success Criterion.

Active User Interface Component Examples

For designing focus indicators, selection indicators and user interface components that need to be perceived clearly, the following are examples that have sufficient contrast.

Active User Interface Component Examples
Type Description Examples
Visual Focus Indicator Visual focus indicator for a link that is a blue (#6699cc) outline around the link. The blue (#6699cc) outline does provide a sufficient contrast with the white (#ffffff) background that is equal to 3 to 1. Example 1
Text Input with border Border line (#787878) against immediate surrounding color of white (#FFFFFF) has a contrast ratio of exactly 3 to 1.
Text input using background colour Text input using a different in background colour to indicate the input.
Text Input with partial border Bottom-border line (#787878) against immediate surrounding color of white (#FFFFFF) has a contrast ratio of exactly 3 to 1. The input also has a very light background, however, it is the bottom border that is intended to convey the nature of the input.

Inactive User Interface Components

User Interface Components that are not available for user interaction (eg: a disabled control in HTML) are not required to meet this color contrast requirements in WCAG 2.1. An inactive user interface component is visible but not currently operable. Example: A submit button at the bottom of a form that is visible but cannot be activated until all the required fields in the form are completed.

Inactive components, such as disabled controls in HTML, are not available for user interaction. The decision to exempt inactive controls from the contrast requirements was based on a number of considerations:

  • Backward compatibility: WCAG 2.0 guidance for 1.4.3 Contrast (Minimum) specifically exempts text or images of text that are part of an inactive user interface component. It would be confusing and inconsistent to exempt text in inactive components from contrast considerations while requiring sufficient contrast for the graphical container the text resides in.
  • Variations in significance: Depending on the circumstances, disabled controls may be intentionally designed to be more or less visible depending on how meaningful a control's disabled state is. Two examples can illustrate.

    1. A control remains disabled only until the user completes a prerequisite task, at which point it becomes active.
    2. A designer uses a standard layout for a number of operations. In one operation a control is not valid and so is disabled, but remains visible simply to maintain a consistent layout.

    The disabled control in the first example offers a more significant cue, and a designer may intentionally decrease the contrast in the second case to de-emphasize its importance.

  • Conflicting needs and desires. Although meaningful information is conveyed by a lower-contrast disabled control (to those who can perceive it), not all users desire an increase in the prominence of disabled controls.
    • Low-vision - some users want to ignore the disabled elements, just focusing on the enabled elements. Other low vision users want to see the disabled items clearly.
    • Cognitive - some people with cognitive differences really want to be able to focus on the active elements (and ignore the non-active elements). If we force stronger contrast on the disabled elements, it will likely be difficult for all sighted people to distinguish what is active (and what is disabled).

A one-size fits all solution has been very difficult to establish, a method of varying the presentation of disabled controls based on user preferences is anticipated as an advancement in future.

Graphical Objects

The term "graphical object" applies to stand-alone icons such as a print icon (with no text), and the important parts of a more complex diagram such as each line in a graph. For simple graphics such as single-color icons the entire image is a graphical object. Images made up of multiple lines, colors and shapes will be made of multiple graphical objects, some of which are required for understanding.

Not every graphical object needs to contrast with its surroundings - only those that are required for a user to understand what the graphic is conveying. Gestalt principles such as the "law of continuity" can be used to ignore minor overlaps with other graphical objects or colors.

Image Notes
An orange circle with a white telephone icon in the middle.

The phone icon is a simple shape within the orange circle. The meaning can be understood from that icon alone, the background behind the circle is irrelevant.

The graphical object is the white phone icon.

A red magnet with grey tips and a black outline.

A magnet can be understood by the U shape with lighter colored tips. Therefore to understand this graphic you should be able to discern the overall shape (against the background) and the lighter colored tips (against the rest of the U shape and the background).

The graphical objects are the U shape (by outline or by the solid red color), and each tip of the magnet.

A yellow arrow pointing down with a pound sign (currency) in the middle.

The low-currency symbol can be understood with recognition of the shape (down arrow) and the currency symbol (pound icon with the shape). To understand this graphic you need to discern the arrow shape against the white background, and the pound icon against the yellow background.

The graphical objects are the shape and the currency symbol.

A line chart of votes across a region, with 4 lines of different colors tracking over time.

In order to understand the graph you need to discern the lines and shapes for each condition. Therefore each line and colored shape is a ‘graphical object’ in the graph and should be over 3:1 against the white background. Most of them have good contrast except the green triangles.

The graphical objects are the lines in the graph, including the background lines for the values, and the colored lines with shapes.

The lines should have 3:1 contrast against their background, but as there is little overlap with other lines they do not need to contrast with each other. (See the testing principles below.)

A pie chart with small gaps between each slice showing the white background, and a dark outline around light colored slices.

To understand the pie chart you have to discern each slice of the pie chart from the others.

The graphical objects are the slices of the pie (chart).

Note: If the values of the pie chart slices were also presented in a conforming manner (see the Pie Charts example for details), the slices would not be required for understanding.

Taking the magnet image above as an example, the process for establishing the graphical object(s) is to:

Due to the strong contrast of the red and white, it would also be possible to only put the outline around the white tips of the magnet and it would still conform.

Required for Understanding

The term "required for understanding" is used in the Success Criterion as many graphics do not need to meet the contrast requirements. If a person needs to perceive a graphic, or part of a graphic (a graphical object) in order to understand the content it should have sufficient contrast. However, that is not a requirement when:

Gradients

Gradients can reduce the apparent contrast between areas, and make it more difficult to test. The general principles is to identify the graphical object(s) required for understanding, and take the central color of that area. If you remove the adjacent colour which does not have sufficient contrast, can you still identify and understand the graphical object?

Two versions of a blue circle with an 'i' indicating information. The first example has a blue gradient background, the second is missing the upper half of the background which obscures the i.
Removing the background which does not have sufficient contrast highlights that the graphical object (the "i") is not then understandable.

Dynamic Examples

Some graphics may have interactions that either vary the contrast, or display the information as text when you mouseover/tap/focus each graphical object. In order for someone to discern the graphics exist at all, there must be contrasting colors or text in order to find the graphics. Within that area, information available by a conforming method (e.g. focusable elements) can be used to make that information available dynamically as text, or dynamically increase the contrast.

A pie chart with one slice highlighted and a box hovering next to it that shows the data and indicates the source in the key.
A dynamic chart where the current 'slice' is hovered or focused, which activates the associated text display of the values and highlights the series.

Infographics

Infographics can mean any graphic conveying data, such as a chart or diagram. On the web it is often used to indicate a large graphic with lots of statements, pictures, charts or other ways of conveying data. In the context of graphics contrast, each item within such an infographic should be treated as a set of graphical objects, regardless of whether it is in one file or separate files.

Infographics often fail to meet several WCAG level AA criteria including:

An infographic can use text which meets the other criteria to minimise the number of graphical objects required for understanding. For example, using text with sufficient contrast to provide the values in a chart.

Essential Exception

Graphical objects do not have to meet the contrast requirements when "a particular presentation of graphics is essential to the information being conveyed". The Essential exception is intended to apply when there is no way of presenting the graphic with sufficient contrast without undermining the meaning. For example:

Graphical Object Examples

  • Status icons on an application's dashboard (without associated text) have a 3:1 minimum contrast ratio.
  • A text input has a dark border around the white editable area.
  • A graph uses a light background and ensures that the colors for each line have a 3:1 contrast ratio against the background.

Pie Charts

Pie charts make a good case study for the graphical objects part of this success criteria, the following pie charts are intended to convey the proportion of market share each browser has. NB: The actual figures are made up, these are not actual market shares.

Failing pie chart

Fail: The pie chart has labels for each slice (so passes 1.4.1 Use of Color), but in order to understand the proportions of the slices you must discern the edges of the slices (the graphical objects conveying essential information), and the contrast between the slices is not over 3:1.

Not applicable pie chart

Not applicable: The pie chart has visible labels and values that convey equivalent information to the graphical objects (the pie slices).

Passing pie chart

Pass: The pie chart has visible labels, and sufficient contrast around and between the slices of the pie chart (the graphical objects). A darker border has been added around the yellow slice in order to achieve the contrast level.

Infographics

An infographic showing lightly coloured circles of various sizes to indicate the size of five different social networks

Fail: Discerning the circles is required to understand the size of network and discerning the icons in each circle is required to identify which network it shows.

The graphical objects are the circles (measured against the background) and the icons in each circle (measured against the circle's background).

The same infographic with contrasting text, dark borders around the circles, and contrasting icons.

Pass: The circles have contrasting borders and the icons are a contrasting dark colour against the light circle backgrounds.

There are many possible solutions to ensuring contrast, the example shows the use of borders. Other techniques are to use darker colours for the circle backgrounds, or to add text labels & values for each item.

Testing Principles

A summary of the high-level process for finding and assessing non-text graphics on a web page:

The techniques below each have testing criteria.

Benefits

People with low vision often have difficulty perceiving graphics that have insufficient contrast. This can be exacerbated if the person has a color vision deficiency that lowers the contrast even further. Providing a relative luminance (lightness difference) of 3:1 or greater can make these items more distinguishable when the person does not see a full range of colors.

Resources

Techniques

Sufficient

Graphics with sufficient contrast

  • Contrasting colors between graphical objects (TBD)
  • Include contrasting lines between adjoining colors (TBD)

Text in or over graphics

Advisory