By Linda Roberts | Senior Member
This column shares information about accessibility requirements and techniques, and introduces standards and policies that might affect your products. If you have feedback, contact Linda Roberts at lerober1@yahoo.com.
As I was catching up on the tweets from the STC AccessAbility SIG (@staccess), I came across a retweet that said, “Spread the awareness for colour blindness. Numbers don't lie.” This tweet had a link to the following pie chart.
The chart made me smile. With simplicity, it brought the message home that when you are building a website or graphic, you should not forget about your users who are color blind. If you want to create an accessible website for all, then you need to take color-impaired users into consideration, because for your users who are color blind, bad color combinations might make navigation and interaction difficult, if not impossible.
The following list is an overview of evaluation tools to help you to assess the color combinations in your websites and images. This list is by no means comprehensive. These are the tools I have used or have heard good things about. For a more comprehensive list of evaluation tools, visit the World Wide Web Consortium's website, where they collect information about evaluation tools (www.w3.org/WAI/ER/tools/).
Vischeck (www.vischeck.com/) is both a free online service and a downloadable application that shows you how your Web page or graphic would appear to a user that has one of three types of color blindness. It also has the ability to correct an image so that it is more usable for a person who is color blind.
Coblist—Color Blindness Simulator (www.colblindor.com/coblis-color-blindness-simulator/) is another free online tool that simulates what an image looks like to a person who has one of eight types of color blindness.
The Contrast Analyzer (www.paciellogroup.com/resources/contrast-analyser.html) by The Paciello Group is a free downloadable application that allows you to check a Web page's foreground and background color combinations to determine whether they provide adequate contrast. You can also select a graphic so that the tool can simulate what the graphic looks like to users who are color blind or have cataracts.
ColorDoctor (www.fujitsu.com/global/accessibility/assistance/cd/) by Fujitsu is a free, downloadable application that simulates what a website looks like to a person who is color-blind. They claim that it can also simulate the “real-time display” of presentation or moving images, such as Flash images, by selecting the “Transparent” mode.
The Colorblind Web Page Filter (http://colorfilter.wickline.org/) is an online tool where you enter a URL and select a type of color-blindness to emulate, and the tool shows you what the page looks like to the selected audience.
Even though these tools are easy to use and are readily available, they do not replace human feedback. When evaluating your websites, conduct usability and accessibility tests with real users so you get their unique perspectives.
Most common types of color blindness:
- Deuteranopia/Deuteranomoly: People have trouble with red/green color deficit due to missing or faulty green retinal receptors.
- Protanopia/Protanomaly: People have trouble with red/green color combinations due to missing or faulty red retinal receptors.
- Tritanopia/Tritanopia: People have trouble with blue/yellow color combinations due to missing or faulty blue retinal receptors.
