Hi,

I have gotten some sentences from an online help titled "Some examples of Colon Usage" from the people.whitman.edu website. Can you tell me how their colon usage is justified? What part of the main clause does it elaborating or explaining?

My wife says every men she's been familiar with would smell his socks at night before he went of bed: just a whiff--each sock, not only one. [Edward Hoagland,  "The Problem of the Golden Rule"]   

I was insisting and reiterating that I was a human being: if I could get that message across to him he would stop shooting at me. [Edward Hoagland, "The Problem of the Golden Rule]

But this sentence was not allowed to spoiled the effect: It was withheld from the press. [Barbara Tuchman, "Perdicaris Alive or Raisuli Dead]

She is knocked out from getting most of us ready: I hold my neck stiff against the pressure of her knuckles as she hastily completes the braiding and then beribboning of my hair. [Alice Walker, "Beauty: When the Other Dancer Is the Self"] 

Opportunism and greed: there you had your much-vaunted corporate business world. [Tom Wolfe, "The Right Stuff"] 

I think the last example could have  been written with a dash.