More than six black tokens cannot be assigned in a round. Later penalties are not accrued.
Trumped tricks can use up a red token or the color of the suit led--if you have many trumps, you can bid your short suits instead of red.
The Saboteur can be a good choice when you are short-suited with a few reds. (In a three player game the Saboteur can be very lucrative, so it costs 5 penalty points to take it in a 3-player game.)