Colons after a single word (e.g. "Example:")
Solution 1:
To build on the point that @BladorthinTheGrey is making, grammar describes the way words are related to form meaning in sentences. But there are other ways to form relationship that express meaning, including page layout devices such as labels or headings, or parallel constructions such as tables.
A word (or a few words) followed by a colon is a common way of attaching a label to a piece of information. This is one of those non-grammatical uses referred to in other answers, and it is non grammatical because it is outside the scope of grammar. (That is, not concerned with the construction of sentences.)
So, Examples: is a label in the example given. It is a common and accepted way to create labels, but it is outside the scope of grammar because it is not part of a sentence construction.
Solution 2:
Below is a copy of an extract from The Punctuation Guide relating to the various uses of a colon.
You will see, at the bottom of the first section "Introducing a list" are examples of usage after a single word: "Correct: " & "Incorrect: ".
Similar usage is also shown in the last section "Correspondence", with a colon being used after a single word or brief 'title'.
The usage you've referred to as "after a full sentence" is illustrated in the sections "Between independent clauses " & "Emphasis"
From: http://www.thepunctuationguide.com/colon.html
Further information is also given in my answer to this related question: Colon after 'Destination'
Solution 3:
According to this guide, colons can be used for emphasis:
The colon can be used to emphasize a phrase or single word at the end of a sentence.
Conclusion: This practice can be followed when that single word is at either end of the sentence.