The oldest usability guideline for any type of navigational design is to help users understand where they've been, where they are, and where they can go (past, present, and future). The three are somewhat interrelated: a good grasp of past navigation helps you understand your current location, since it's the culmination of your journey. Knowing your past and present locations in turn makes it easier to decide where to go next.
On the Web, links are a key factor in this navigation process. Users can exclude links that proved fruitless in their earlier visits. Conversely, they might revisit links they found helpful in the past.
Most important, knowing which pages they've already visited frees users from unintentionally revisiting the same pages over and over again.
The Price of Uniform Link Color
Generally, Web browsers are severely deficient in supporting user navigation. However, they do provide one feature that helps users orient themselves: browsers let designers display links in different colors, depending on whether the links lead to new pages or pages that users have seen before. Changing the color of visited links has been part of Web browsing since Mosaic arrived in 1993, so it's completely standard; almost all users understand it.
Currently, 74% of websites use different colors for visited and unvisited links, making this design approach a strong convention that people have come to expect.
Hypertext theory, the Web's history, and current design conventions all indicate the need to change the color of visited links. Further, empirical observations from user testing have identified several severe usability problems on sites that violate this convention. When sites use the same color for visited and unvisited links, users:
unintentionally revisit the same pages repeatedly;
get lost more easily because their understanding of each link's meaning is reduced;
often misinterpret or overlook the difference between two similar links if theyre unsure about which one they've already visited; and
give up faster because they have a reduced sense of mastery when the site fails to reflect their actions and thus help them navigate.
Such usability problems are particularly damaging to users with weak short-term memory, who often have trouble remembering what they've clicked without a visual representation. Of course, "weak short-term memory" is an inherent shortcoming of all humans, which is why all users are harmed by unchanging link colors. But this definitely impacts some people more than others, so it's particularly important to change link colors if you have many older users.
Given the extensive theoretical and empirical support for using different link colors, it's astounding that a quarter of all websites continues to inflict extra usability problems on people by choosing a uniform link color.
Why the Problem Persists
Even people who believe in usability sometimes question the need for changing link colors. I think this is because they don't pick up on the problems caused by unchanging links when they conduct their own user testing. Unfortunately, the symptoms of these problems are among the most difficult to detect when you observe users.
User testing is basically easy: we teach it in 3 days. Most important usability problems are so glaring that anybody can identify them through a simple test. Once you know the basics of how to write good tasks and how to facilitate the session without biasing user behavior, you can clearly see users get into trouble when they encounter poorly designed components of your site.
Say, for example, that a user clicks the wrong button. It's obvious to any observer that such behavior represents a design error. Listening to users' comments prior to clicking usually tells you why they misunderstood the design, thus guiding you to make it better in the redesign.
Cases in which users don't do something are harder to discover. Even so, most usability facilitators can identify many such problems. You might, for example, observe that no one in your test clicked on one of your major features. Users' thinking-aloud comments will make it clear whether they (a) saw the feature, but didn't find it relevant; or (b) never considered the feature because it looked too much like an advertisement.
Detecting Distributed Usability Problems
Some usability problems require more detective work and are often overlooked by people relatively new to user testing. This is particularly true for problems that are a composite of multiple individual issues scattered around the site. Identifying these problems is even more difficult when none of the individual issues cause difficulties on their own.
A relatively simple example of a multi-location problem is when a homepage link sets certain expectations that cause users to misinterpret the information on the destination page. The link text itself might be clear, and users are unlikely to complain about it. The destination page might also be clear, and users might not complain about it, either, because they think they understand it. The problem is that they understand it wrong because they interpret it in the context of their misguided expectations. This type of usability problem requires test observers to make high-level conclusions based on remembering what happened on the previous page, even though nothing that happened seemed to cause users difficulties.
The damage that unchanging link colors cause is one of the most tricky usability problems to identify in user testing. On any given page, users seem to understand the links just fine. Users almost never complain about link colors, as long as they're distinct from the rest of the text and reasonably legible. Life is good, or so it seems.
Observe carefully, though, and you'll notice that users frequently move in circles. They'll visit the same page multiple times — not because they want to, but because they don't realize that they've already been there. Users will give up when they've tried most links in a list, even though there's one link that they haven't tried; if the links don't change colors, users don't realize that there's only one unvisited link remaining.
Unchanging link colors also create navigational confusion because users don't quite understand their different choices or where they are. Of course, this problem could also be a symptom of muddled information architecture or poorly written labels, which is why it requires experience to identify the true root cause of the users' difficulties.
Even though the downsides of unchanging link colors are easily overlooked in user testing, they're very real and problematic for users. Many other design strategies for helping users navigate, such as site maps, require a good deal of work. But the browser lets you change link colors for free, so there's no reason not to take advantage of this simple way to help your users.
Using different colors for visited and unvisited links makes your site easier to navigate and thus increases user satisfaction.
Next week's Alertbox features detailed guidelines for textual links, including advice about the actual colors to use for visited and unvisited links.
The reports on Intranet Navigation Guidelines and Intranet Information Architecture (IA) have more information about these issues, as they relate to intranets.
Full-day training course on Navigation Design at the annual annual Usability Week conference.
The conference also has a full-day training course on Web Page Design.