Thanks for the explanation Paul. I think I'm catching on....
The HS20 has typically been reported as a projector that exhibits a magenta "push". Some have theorized that the magenta-tinted lens cover causes this, others say it's the bulb, still others have suggested poor factory calibration.
After reading your explanation and reading on ProjectorCentral.com that the HS20 is optimized for an HD signal, I seems I should conclude that SD signals fed into the HS20 would exhibit a magenta hue (or a green depression). And, I would draw this conclusion by combining the magenta issues I've read with your explanation above.
Their is some confusion that remains. In your description of how to deal with this green depression issue, you say that facial tones would appear "jaundiced". To me, excessive green creates a jaundiced appearance (because it yellows the skin). If correctly understand the issue, I would anticipate that facial tones would appear overly red (or magenta-tinted). This seems the opposite of what you're saying. Hopefully, it's just that our definitions of a jaundice appearance are different.
And, for those units that do not have a SD/HD color space selector -- but do possess individual red/green/blue adjustment controls, I offer an alternative solution (vs. adjusting the 975).
A recent set of HS20 calibration numbers I received are as follows:
R Gain: -11 R Bias: -6
G Gain: 0 G Bias: 5
B Gain: -23 B Bias: -18
The numbers above were recorded using "Colorfacts and the numbers seem to support the magenta push (green depression) issue you've described in your posts. Unfortunately, the source used for calibration was not specified. Fortunately, the HS20 allows multiple stored user settings!
My conclusion would be that the calibration above was done using a SD signal -- wherease a HD signal might perform closer to factory defaults. And, finally, your measurements/observations regarding the 975 would indicate that settings similar to those shown above may be fairly appropriate when connecting the 975 to a Sony HS20.
Thank you for this enlightenment!