Grammar

[Ouch!]

I'll quote the rules for colon and dash usage from The Elements of Style. "Use a colon after an independent clause to introduce a list of particulars, an appositive, an amplification, or an illustrative quotation." This instance would qualify as an amplification, so a colon would be acceptable. Using a colon in this manner, however, has become quite uncommon. I would suggest that you use a semicolon instead, as it seems to have completely eclipsed colon usage for this purpose.

Strictly speaking, the only incorrect punctuation listed above is the comma which must be used with a conjunction. Otherwise, it's a comma splice. The use of a dash is arguably acceptable, depending on your intent. "Use a dash to set off an abrupt break or interruption, and to announce a long appositive or summary." Depending on how you intend the second independent clause to be read, using a dash would be appropriate.

Anyway, of the options given, I'd use a semicolon, although both the colon and full stop are also acceptable.

Edit: Do not capitalize after the colon.