I mean the colon in writing you manuscript, is there a specific time to type in a colon? I reading A Clockwork Orange, and noticed some of the grammar was a little iffy, but sometimes I notice colons being used for this:

Specific paragraph:

Is this an incorrect way to use it? I don't ever tend to use a colon when I write the paragraphs I generally do, and I know grammar rules have changed a little bit over the years.