i believe this is due to the 60 Hz Flash the bulb emits....i've caught this effect on camera before too.

Yeah it probable is.

Yup, your camera likely captured the picture at almost 0V in the AC cycle.

Whats odd is that my camera does show the true colour of mercury lamps (not making them looks green)

Too fast shutter it fired, when there was no current section.
And i guess you are using CWA ballast - because this type has quite long "pause" between 120Hz "flashes". On HX transformer or series choke reactor you would not hit the really dark region, as it is too short.

Yep its a CWA.

Here is my catch of my Philips ML 160W when there was no current section between the 100hz flickering.

When thinking about what ballast has the long dark "hole", i had the resistive type in mind, but i forgot, then it is actually used as well, in SBMV...