Oh, the colon. Just understood enough to be dangerous. The semi-colon? Not understood much at all and so not dangerous. But the colon? Lists, right? Easy. Not so much. The colon is going the way of the comma in that it is adopting subjective, if incorrect, usages, as in the above example.
I get it. You have the list and you want the pause. Definitely not a comma, and so the colon. But the colon can’t (nor really can any punctuation mark) interrupt the flow of an otherwise discrete grammatical unit. Without the colon, the sentence would read quite naturally, “We want to be the hardest working,….” That is a perfectly correct grammatical sentence and to insert a punctuation mark is only to interrupt that.
More interesting about this example, perhaps, is that it is a transcribed quotation, meaning that the insertion of that colon was an editorial decision. Perhaps the speaker paused long enough that the writer / editor wanted to call attention to that pause, but an ellipsis would seem to do that more elegantly, while still maintaining correctness.