Utter bullshit. The original background color of websites was #c0c0c0, the same default color grey used in desktop apps. It was a big to-do, switching that default. The reason most sites are blue is because the human eye is better able to distinguish shades of blue. Also, a significant % of people are red/green colorblind.
> The reason most sites are blue is because the human eye is better able to distinguish shades of blue. Huh? It's shades of yellow/green that we are best able to distinguish. We're not good at blue.
I'll refer to a cool demonstration of this in action: http://news.ycombinator.com/item?id=1891753
It's not scientific, but it's certainly telling.
TL;DR: Green is the color we see well.