I'm not sure about the color problem, but you assume correctly that the line cord is supposed to be captive in the cabinet back so it disconnects when you remove it. There is usually a squared-off C clip inside the cabinet back that's pretty easy to pry out. You can kind of see one in place
here.
Your set has the HE chassis, which is somewhat improved from the very first version, and I believe also has an all purpose-made CRT instead of the first-generation's 25-inch shadow mask that was cut down to make it fit. The Sams is 1384-1.
Those sets suffer from bad solder connections on the PC board; you might try tapping around on it and see what you can turn up.