The question is in the subject. I've noticed that some MH lamps have much less bright electrodes during ignition than others.
For example: My Osram HQI-TS 70W/WDL Excellence, have much dimmer electrodes than my Osram HCI-TS 70W/WDL. Another comparison is with blue and green MH lamps. With my green 70W MH lamp, its electrodes barely glowing during ignition, compared to the intense glow of the electrodes of my 70W 20000K and 14000K MH lamps
Why this is happening?

Someone? @RRK? @James? @Medved?

Different lamp design engineers, different result. This is a thing which has more than just one single "right solution", so it would be rather strange when all would behave exactly the same.
My bet is, there are just few different electrode designs in use, different in operating temperatures (special emission materials vs just higher operating temperature of base tungsten, different strategy to get desired compromise between sputrtering due to the electrode being too cold vs evaporating when too hot,...), the way how the electrode is cooled, how the temperature is regulated. Even for equivalent lamp (from its rating perspective), each exact model may differ and use different approach/strategy how exactly it is designed. Big factor is the target use scenario, which ballast, use pattern,...
And the differences in designs mean the behavior will differ, mainly on aspects that are of zero importance for the application.

Green MH lamps often have barely glowing electrodes, compared to the brightly glowing electrodes of blue MH lamps.

Also, this likely depends on buffer gas pressure and contents. Mercury and old-school 3-electrode MH lamps use low-pressure argon to keep ignition voltage low, more modern pulse start lamps have much higher pressures and probably some exotic gases like Kr or Xe. Lower pressure means higher speed of ion bombardment and less thermal conductivity of the gas, so higher electrode temperature.

We (neon makers) use this effect for the purpose when 'internally bombarding' neon tubes. If bombarded under 3-6mmHg of the air fill, voltage drop of the discharge column is increased, and tube body glass is heated preferentially, with electrodes keeping rather cool, at the end of process, air fill pressure is pumped down to 1-2mmHg and electrode shells are started to heat up preferentially.