Mission impossible VS. Impossible mission

Mission impossible VS. Impossible mission

While I tried to find out which one is correct in grammar, I realized that the real title is 'Mission: impossible' and then I have two questions.

I think that Impossible mission is grammatically correct or both are acceptable and they mean the same?
And the usage of colon in the title is correct and then which rule should I apply to it?

Colon

A colon is used to give emphasis, present dialogue, introduce lists or text, and clarify composition titles.
Emphasis—Capitalize the first word after the colon only if it is a proper noun or the start of a complete sentence. (She had one love: Western Michigan University.)
Dialogue—Write the speaker's name, followed by a colon and his or her statement. (Reporter: What is the Western Edge? Dunn: It is a strategic plan for promoting student success.)
Introduce lists, text or tabular material—Capitalize the first word after the colon only if it is a proper noun or the start of a complete sentence. (Our future is dependent on three things: sustainability, diversity, and enhancing our strength and health.)
Clarify the titles of books, lectures and other compositions—Use a colon in titles that express two parallel ideas. The words on either side of the colon should be able to stand on their own. (He wrote "Crisis Management by Apology: Corporate Response to Allegations of Wrongdoing.")

Thank you so much as usual!