If the comments from users on Twitter, Reddit and Google's forums are any indication, it is not likely that the changes will be rolled out across the board any time soon.

Other than the red links it uses in China, and different shades of its blue Google has not used other colours for its search results before.

A spokesman for Google said the company is "always" testing small changes to its results page. On this occasion, Google admits, "We're not quite sure that black is the new blue."

Google is not the only major technology company to carry out A/B tests on its users. Netflix recently admitted that it tests six different images for many TV and movie titles, and rolls out the one that most viewers click on.

Facebook has also conducted tests designed to emotionally manipulate users by highlighting positive and negative emotions, while OK Cupid has deliberately matched incompatible people to see the outcomes.