I've been looking further at Plasma calibration, and it really is very, very difficult due to the operation of ABL, which can't be turned off.
(ABL is Automated Brightness Level/Control - all plasmas have this, and it can't be turned off).
The above image shows the RGB Separation for a Panasonic plasma profiled yesterday. Profiling was with a very small patch size - approx a 20th screen area, in an attempt to limit the ABL effect.
What you can see is that the ABL kicks in immediately, not after a given level.
The 45deg line shows what is expected - the RGB plots show the variation of RGB values for the grey scale compared to the expected.
So, this means that a patch that is just R, G or B has a great saturation than the equivalent grey patch, meaning that saturation will always be greater for a given value of input compared to the expected value based on the display's grey scale (which is a simple mathematical combination of RGB for a given colour space).
The end result?
A plasma can only ever be close to accurately calibrated by a 3D LUT that can deal with the poor RGB separation - but even that cannot totally override the ABL operation.
Hope this helps with some level of understanding of Plasma calibration issues.
Mob Boss at Light Illusion