I'm not sure if this is a new quality, but it's pretty useful. Like most websites, Google's search engine changes the color of visited links from blue to purple. All browsers grip links this way by default, but websites can alter the colors using some CSS code.
If you're logged in using your Google Account and Web History is enabled, Google saves all the search results you visit to your Web History. When you're using a different browser or a different computer and you're logged in using the similar account, Google changes the color of the visited links from blue to purple, irrespective of the browser or computer you've used to visit them. For example, I searched for [haploid] using Chrome, I clicked on one of the results, then I tried the same query in Internet Explorer and the page I've visited in Chrome previously had a purple link.
Google also has a search filter that lets you limit the results to visited pages. Just click "More search tools" in the sidebar and select "Visited pages". For pages you're visiting regularly, Google shows an explanation below the snippet: "You've visited this page X times. Last visit: ...". When you mouse over the snippet, Google suggests to +1 the link: "You've visited this page X times. +1 to suggest it on Google search!".