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Ensuring proper color contrast

From: Web Accessibility Principles

Video: Ensuring proper color contrast

>> The size of the text and its ability to resize is not the only aspect of its style that effects how easy it is to read. The amount of contrast its color has compared to the background color is also very important. Let's look at how color contrast is measured, see if our page has sufficient color contrast so far and make changes where necessary. Color contrast is not specifically mentioned in section 508, but it is part of WCAG 1.0 and 2.0. in WCAG 1.0 the standard states ensure that foreground and background color combinations provide sufficient color contrast when viewed by someone having color deficits of when viewed on a black and white screen.

Ensuring proper color contrast

>> The size of the text and its ability to resize is not the only aspect of its style that effects how easy it is to read. The amount of contrast its color has compared to the background color is also very important. Let's look at how color contrast is measured, see if our page has sufficient color contrast so far and make changes where necessary. Color contrast is not specifically mentioned in section 508, but it is part of WCAG 1.0 and 2.0. in WCAG 1.0 the standard states ensure that foreground and background color combinations provide sufficient color contrast when viewed by someone having color deficits of when viewed on a black and white screen.

No actual measurement is given in the standard so we have no way of knowing what sufficient contrast means. There are a couple of ways of measuring color contrast that are currently being proposed. WCAG 2.0 sets a luminosity ratio that must be met. It states that the contrast ration of text and background must be at least five to one, except if the text is pure decoration. For larger scale text, which is text that is 18 points or larger, or if it's bold, 14 points or larger, it could have a ratio of three to one.

Another working group within the W3C, the Accessibility Evaluation and Repair Tools, or AERT, developed their own way of testing color contrast by looking at the difference in brightness and the difference in color. AERT recommends a difference in brightness of greater than 125 and a difference in color of greater than 500. It's not important to know the actually algorithms used to measure color contrast in both of these standards as we can use the analyzer tools that we downloaded and bookmarked in an earlier chapter to test this.

Remember also that neither one of these are recommendations yet, so you don't have to comply with them, but they are useful to look at so they give us concrete numbers to test with and get an idea if our text is pretty high contrast or pretty low contrast and we can start preparing for whatever standard is ultimately adopted. If you're following along with the exercise files, open the page visitors.html in Firefox. It's in the 04_07 folder of the chapter four exercise files. This is the same page that we've been working on throughout this chapter.

Let's take a break from styling this page to check our existing styles and see if they meet color contrast guidelines. We can use the color contrast analyzer extension that we previously downloaded into Firefox to test this. To access the tool, right click if you're on Windows or control click if you're on a MAC, on the page. This brings up a Context menu. Scroll down and select color contrast analyzer. You have the option of testing against both of the guidelines that we just talked about. Let's choose all tests.

This opens a new tab with the results of our test. Every text element on the page is analyzed for its contrast between foreground and background. The names of the elements that were tested are listed along the left side of the results table. You can also see a sample of the foreground and background colors used for each element. Any elements that do not pass all three of the test will have a yellow highlight to their row in the report. The details of which tests we passed and failed are given in the last three columns of the table.

It passes the luminosity contrast ratio tests. It also passes the difference in brightness test. But, if fails the difference in color test. However, it's very close to the guideline value of 500, so we might not have to change the color values too much in order to pass this test. Scroll down the page to see all of the results. The second row from the bottom is for the heading within the footer. We're not going to worry about passing or failing its test since it is not visible on the screen.

Other than that heading, most of these headings are pretty close to the values needed to pass, so let's go into Dreamweaver and change our color values just a little bit to see if we can make the contrast a little bit greater. I have the same file, visitors.html, open in Dreamweaver. Open the CSS styles panel and scroll through the list of styles at the top. Choose the H1 rule. We need to modify its color, so click on the color value.

Highlight over the numbers that are currently being used and delete them then type 195F6E. This color is also from the logo of the site, the darker color used in the flowers of the logo. Hit enter or return to accept this value. You can see that our H1 text is now a little bit darker. Go back into the CSS styles panel and click on this color again. Hit control C or command C on your keyboard to copy the value then click on the H2 rule above, now select its color value and hit control V or command V to paste in the new value.

Finally, select the H3 rule above. Click on its color value and again press control V or command V then press enter or return to accept the value. Scroll down the page in design view to see the change in our headings. The color isn't too far off from what it was set to before, but it might be enough to help us pass all three tests. Go to the File menu and save the page.

Then go back to Firefox, click on the tab where the visitor's page is still open and hit the reload button for it to show the new changes to the page. We can now run the color contrast analyzer again. Right click or control click on the page and select color contrast analyzer from the menu then all tests. This time you can see that the only row highlighted in yellow is the header and footer.

Since this is not visible, we don't need to worry about it. We've passed all the other tests for all the other text on the page, so our page is now at a point where it has the basic structure and styles for the text in place and tested. There are a number of other HTML elements related to text that we can add to the page to enhance its accessibility. In the next few movies we'll go over the HTML for creating emphasized text, quotations and lists.

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This video is part of

Image for Web Accessibility Principles
Web Accessibility Principles

68 video lessons · 25805 viewers

Zoe Gillenwater
Author

 
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  1. 2m 0s
    1. Welcome
      1m 3s
    2. Using the exercise files
      57s
  2. 33m 15s
    1. What does accessibility mean?
      5m 51s
    2. How does accessibility help your users?
      3m 30s
    3. Experiencing a website via a screen reader
      5m 46s
    4. How does accessibility help you and your clients?
      3m 9s
    5. Overview of Section 508 standards
      5m 51s
    6. Overview of WCAG standards
      6m 4s
    7. Understanding consistency and semantic markup
      3m 4s
  3. 54m 31s
    1. Understanding screen readers and accessibility tools
      6m 12s
    2. Getting accessible browsers
      5m 41s
    3. Customizing Firefox for accessibility testing
      5m 53s
    4. Using custom accessibility toolbars
      5m 28s
    5. Using Fangs and the Color Contrast Analyzer
      5m 30s
    6. Accessibility tools to bookmark
      5m 53s
    7. Using automated accessibility checking tools
      4m 57s
    8. Setting up the JAWS screen reader on Windows
      6m 42s
    9. Using the VoiceOver screen reader on Mac OS X
      5m 52s
    10. Setting Dreamweaver accessibility preferences
      2m 23s
  4. 26m 12s
    1. Avoiding tables for layout
      3m 30s
    2. Using CSS for layout
      2m 40s
    3. Creating a fixed-width layout
      5m 51s
    4. Creating an elastic layout
      3m 51s
    5. Creating a liquid layout
      3m 4s
    6. Customizing a liquid layout
      7m 16s
  5. 1h 6m
    1. Specifying the language
      3m 43s
    2. Setting page titles
      2m 16s
    3. Setting headings and paragraphs
      9m 55s
    4. Styling headings
      9m 56s
    5. Hiding section headings from sighted users
      6m 41s
    6. Styling text for readability
      6m 41s
    7. Ensuring proper color contrast
      6m 36s
    8. Creating text emphasis
      4m 29s
    9. Indicating quotations
      4m 29s
    10. Creating basic lists
      4m 16s
    11. Styling lists
      7m 15s
  6. 1h 15m
    1. Using lists for navigation
      6m 45s
    2. Creating a horizontal navigation bar
      13m 25s
    3. Creating a vertical navigation bar
      11m 44s
    4. Adding skip navigation links
      12m 0s
    5. Hiding skip navigation links
      6m 17s
    6. Proper link text and title attributes
      6m 11s
    7. Opening new windows
      4m 28s
    8. Accessibility limitations of fly-out menus
      6m 30s
    9. Creating an accessible fly-out menu
      8m 38s
  7. 27m 55s
    1. Proper ALT text for navigation images
      4m 57s
    2. Proper ALT text for decorative images
      5m 19s
    3. Adding ALT text to an existing site
      6m 9s
    4. Adding ALT text to image maps
      5m 58s
    5. Describing complex graphics
      5m 32s
  8. 34m 1s
    1. Using tables for data
      3m 0s
    2. Creating header cells
      4m 5s
    3. Adding table captions and summaries
      9m 9s
    4. Styling tables
      5m 19s
    5. Applying header cells to complex tables
      6m 52s
    6. Adding id and headers attributes
      5m 36s
  9. 42m 7s
    1. Understanding form accessibility issues
      3m 7s
    2. Labeling form fields
      6m 9s
    3. Adding fieldsets and legends
      4m 42s
    4. Moving forms out of tables
      3m 44s
    5. Cleaning up a form's appearance
      4m 53s
    6. Aligning labels and fields using CSS
      9m 39s
    7. Indicating required fields
      6m 15s
    8. Dealing with CAPTCHA
      3m 38s
  10. 7m 29s
    1. The Text-Only technique
      3m 21s
    2. The Access Keys technique
      2m 35s
    3. The Tab Index technique
      1m 33s
  11. 18s
    1. Goodbye
      18s

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