Colors play a vital role on providing a good visual appearance on web pages. Good combination of colors provides enhanced user experience. While designing accessible web pages designers assume that use of certain colors harm people with disabilities. Is it true? Let us understand.
Visual challenges can be broadly divided as blindness, low vision and color blindness. Let us understand the problems of users effected by each of them, how do they impact while interacting with web content.
Users with blindness
Users who are blind operate computers with screen readers to perceive the web content. For these users care should be taken that the important information that is conveyed through color need to be provided by additional qeus. This additional qeus can be either provided by content or can be programmatically determined.
For example the red color for mandatory fields can be supplemented with ‘*’ symbol. An inactive button can be informed to the screen reader user by setting aria-disabled to true to the button.
So, the conclusion is designers are recommended not to compromise on colors for blind users.
Low vision
A low vision user can see and read the web content but they may need enough contrast between the content and it’s background. It might be difficult to read a blue content on black background. Designers are encouraged to use any color they prefer to but primarily the colors used should not restrict the users from reading the content. Using enough contrast between the foreground and background is important. 1.4.3 Minimum (contrast) explains briefly on WCAG 2.0 requirement for color contrast. It is important to check the contrast for text on images when an important content is provided on them.
So, for low vision any color can be used but ensure that a minimum contrast is maintained between the foreground and background, links and their surrounding content.
Color Blindness
Color blindness is mainly of four types. Protanopia, Deuteranopia, Tritanopia and Rod monochromacy.
Protanopia
Protanopia is also called as red-green color blindness. Protons may have either defective long wave length cones (L-cones) or no l-cones at all. The missing of l-cones is called as Protanopia and a defective l-cones is called as protanomaly. People effected with Protanopia and protanomaly have hard time in distinguishing between red and green colors. They can differentiate dark red and light green comfortably than differentiating dark red and dark green.
Deuteranopia
Deuteranopia is also called as red-green color blindness. Deutan color vision deficiencies are most common forms of color blindness. Deutan color vision deficiencies, which again are split into two different types. Deuteranopia (also called green-blind). In this case the medium wavelength sensitive cones (M-cones) are missing at all. Deuteranomaly (M-cones-weak). This can be everything between almost normal color vision and deuteranopia. The green sensitive cones are not missing in this case, but the peak of sensitivity is moved towards the red sensitive cones.
Tritanopia
Tritanopia is also called as blue-Yellow Color Blindness. Though Tritanopia is called as blue-yello color blindness, people effected with Tritanopia face difficulty in differentiating blue and green colors. Tritan defects affect short-wave length cones (s-cones). The two different types of Tritanopia are,
Tritanopia: People affected by tritanopia are dichromats. This means the S-cones are completely missing and only long- and medium-wavelength cones are present.
Tritanomaly: This is an alleviated form of blue-yellow color blindness, where the S-cones are present but do have some kind of mutation.
People affected by Tritanopia are very rarely observed.
Rod monochromacy or achromacy (no color)
Rod monochromacy is very rarely seen in general. People affected by Rod monochromacy can only differentiate between light, dark and some shades of grey. In this case user vision relies solely on the rods and the cones are usually not working at all.
Information from Color Blindness
Coming back to web content, users with Protanopia, Deuteranopia and Tritanopia can perceive some colors , however If necessary consider provide good contrast while using red and green colors. Users with Rod monochromacy cannot perceive color at all. For these small set of users alternate way of identifying information conveyed through color should be provided similar to what is provided for a blind user.
So, even in this case designers are not required to compromise in using colors.
Conclusion
Designers should not compromise using any color while designing for accessibility. They just need to concentrate on contrast and alternate way for colors purposefully used. It is just a myth that only certain colors should be used for accessibility.