There are two schools of thought regarding post-colon capitalization (sounds like an awful surgical procedure, doesn't it?). In general, it's a style issue that depends on what is following the colon.
Some grammarians recommend capitalizing the first word after a colon if it introduces something akin to a complete sentence.
The less conservative free spirits tell you to never capitalize after a colon. This rule is easier to follow… unless the first word is supposed to be capitalized in the first place (like, if it's a proper noun), you know to always leave it lowercase.