For the colosseum, did you choose the "print at home" option or pick up at the box office? If you chose to print at home you don't need anything else. Just show the attendant at the front of the line and he will direct you where to go. You don't wait in any line because you already have a ticket.
If you chose to pick them up at the box office, again, show the attendant. He will put you in the right line. There may be one or two people in front of you picking up their tickets but it only takes a minute. They look up your reservation and the tickets print right out. You won't lose any time doing this.
You can only pick up these tickets at the colosseum so going to the palatine hill will get you nothing if you didn't choose the "print at home" option.
Donna