craigslist silvertone roundie

[ChrisW6ATV]

That control sounds like a decades-early version of what is now a common option on TV sets: Adjustable color temperature. Aside from, yes, being another way to misadjust the picture, it does have (on modern sets, at least) a very valuable function: To change the temperature from "TV white" (9300 degrees K) to real white (6500 degrees K, as used in the TV studios). TV sets "out of the box" are set up for blazing-bright pictures to help sell them in store displays (and indeed, to some customers who actually like them that way), and one of the tricks was always to make whites bluer. Only when adjustable color temperature returned could users fix this problem without often going inside the set to find the adjustments if they were even available (once they had disappeared from the back panel).