How much space should you put after a colon?

One space.

During the typewriter days, the standard was two spaces after the colon, period, etc. That made sense then: typewriters used a fixed-pitch font, which really needed two spaces of separation. 

But the typesetting standard has always been one space after all punctuation—including the colon. On a computer, you're doing typesetting, so use one space.

Do you think only one space after a colon looks funny? Well, virtually every book, magazine, and newspaper you've read during your lifetime has used only one space!