I thought this was something to do with pornography, but no. Not depression, either. Actually blue:
The blue at the top of this post [on the original site] is a Google blue. It’s not the only Google blue, just the Google blue you see the most. How was it chosen? Another blue, a slightly different Google blue, the story goes, was selected by a designer who liked how it looked. But this designer was told by a manager that this blue was the wrong blue: Another blue, testing revealed, had resulted in more clicking. Their boss intervened. 41 blues, between the nice blue and the powerful blue, were tested for efficacy. One prevailed.
Internet, Why So Blue? John Herrman, The Awl (27 June 2014)
The Awl’s full article shows those blues and you’ll be surprised how readily you recognise Google’s and Twitter’s and Facebook’s shades of the colour. But it’s also interesting because it includes a nod to a time when there wasn’t a word for blue – and to the moment that someone decided underlined links on the web should be and would be blue.