Should I put a capital letter after a colon?

No, in most cases.  Yes, when the passage that follows is a full sentence and is longer than just a few words.

For example:  We cannot recruit any additional staff at the moment for one reason: our budget has been used up. And: The committee must find solutions to three problems: poor visibility, damage to equipment, and irregular transportation schedules.

But:  One fact about American cars should not go unnoticed: They are designed for transportation needs in a country larger than all of Europe.

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