Have you run across the situation where one sentence ending with a colon is followed by another sentence? Do you capitalize the first word of that second sentence? Why would you use a colon between the two sentences rather than a period or a semicolon?
Rule for colons between sentences: Use a colon instead of a [...]

The definition of an appositive is a word or word group that defines or further identifies the noun or noun phrase preceding it.
Rule: When an appositive is essential to the meaning of the noun it belongs to, don’t use commas. When the noun preceding the appositive provides sufficient identification on its own, use commas around [...]