I've owned an awful lot of ethernet cables in my life, in all sorts of colors. Black, blue, white, grey, yellow, green… even brown and red, I'm pretty sure. If you asked me what's the most common ethernet cable color outside black and white, I'd probably go with blue—but this weekend I learned that when ethernet was first designed in the 1970s, the first cables to use it were all yellow, for two primary reasons.
The first was that one of ethernet specification's creators, Rich Seifert, really liked yellow.