The correct answer is "I have one problem with the ski trip this weekend: I can’t ski!". A colon means "that is to say" or "here's what I mean." Colons and semicolons should never be used interchangeably. There are three main uses of the colon:
- to introduce a list
- before a quotation, and sometimes before direct speech
- between two main clauses in cases where the second clause explains or follows from the first