The material following the colon begins with a capital letter if it is more than one sentence long, a formal statement, or a quotation.
Follows the salutation in a business letter or address:
Alumni and Friends:
Introduces a list or series:
You will need the following: scissors, tape, glue, and paint.
Wrong: You will need: scissors, tape, glue, and paint. (no colon between verb and rest of sentence)