On a related subject... I remember reading long, long ago
that the first RCA color TV had /four/ controls for adjusting
the color, which the author described as a "combination lock"!
Anyone know anything about this?

He may be talking about the three 'drive' controls that set the
gain for each channel. These are set up to provide equal gain
to get a white line during setup. They are service adjustments
on TVs, but on an early design they may have been easier to get to.

No, these were supposedly user controls. Anybody got a photo of the user
controls for a CT-100?