There can of course be more than one reason in favour of a decision, whether conscious or unconscious, yet more against bad alternatives (so they get rejected before we even see them) and hence I reckon the other answers here are also partially true. Indeed, quite likely so, since there's an answer here that talks about TimBL while I'm going to talk about Mosaic, which was independent from him.

One stated reason for Mosaic choosing the colour, is that 4-bit colour was still common, and so designs would need to consider how well they would look on such displays. Most such displays used two sets of colours, one of which was of the sequence:

0) Black 1) Blue 2) Red 3) Magenta 4) Green 5) cyan 6) yellow 7) white

(Note the fun way the mixing of colours and adding of numbers has the same results).

Then there would be another set of the same colours, but lighter (sometimes "light black" would mean grey, sometimes "dark white" would mean grey, sometimes both).

Of this sequence, the colours were darkest to lightest in that order (still true of the equivalents in sRGB, NTSC and other richer colour-spaces, though the exact proportions are generally different). Indeed the scheme was designed so you could depend on different relative shades when used with a monochrome display (black and white, black and green or black and orange).

Hence the darkest colour other than black (already used for normal text) that therefore offered the next-greatest contrast against a white or (as used by said Mosaic browser) grey background, was blue. Hence what would later (when attributes for describing colours where added to HTML) be called #0000FF was the standard link colour. (#000080 would also have been available, but not as distinguished from the black of unlinked text).

Red is well-known as a means of emphasis, it would be an appropriate choice for an active link (and was used as such, though I'm pretty sure not until later on, with Netscape Navigator 2.0 if memory serves, since before &lt;frame&gt; and javascript an active link didn't mean much as the page was going to unload anyway), but inadvisable for a visited link, which if anything should be de-emphasised compared to unvisited. After red, the next brightest colour, and so the next most appropriate for text other than blue and black was magenta, but the darker #800080 (purple) was sufficiently different to both blue and black to be distinguished from them, and again the darker choice and hence that which stood out best against a light background.

Why do read links turn purple?
I have a new MacBook Pro, when I'm using it the screen goes suddenly blank for a second and comes back, it feels like as if someone unplugged my screen and plugged it back immediately.. why does this happen? 

Initially I thought it was only happening when I'm running on battery, but happens even when I'm connected too.

This is very sporadic. 
