You are conflating what Gossen does specific to metering color balance for photography with the definition of color temperature, and assuming that their method is the only one used. Gossen chooses one way to do it that works well with three layer color film, and their meter does measure green relative to magenta (a mix of both blue and red). Their method isn't the only way to measure color temperature.
Originally Posted by Leigh B
However, your statements about measuring color temp with only blue and red, disregarding green are simply wrong, and misleading.
Astronomers measure color temperature with Ultraviolet, Blue, and Visible (green-yellow) passband filters, that don't reach deep into red. And yes, they do use green wavelengths as a component to measure color temperature. That's where the V component filter peaks in sensitivity.
You can also use a spectrograph to measure color temperature, which includes green components.
It's nice that you taught color theory. My mom, who is an artist, taught me additive and subtractive color theory when I was a child. I've also used a Minolta color meter for commercial/advertizing photography on location and in the studio.
I also wrote and taught curriculum for physics labs on color temperature at a top ranked college, which was reviewed and also taught by physicists with Ph.D.s from Cornell and U.C. Santa Barbara.
You should recognize that there is more than one way to measure color temp, and that stating that it's always and only a blue-red ratio is wrong.