1. The colored dots just identify the blades for maintenance purposes.
2. 2/rev and 4/rev are vibration modes
3. Governor low side can lead to a crash, which is an almost meaningless thing to say because crashes can happen with two perfectly good engines.
4. B412 has a flex beam yoke attaching the blades to the mast. So it won't bump in the way a teetering rotor can bump the mast. Sure, you can chop the tail boom with the main rotor if you do something whacky, but that would be very rare.