1986 RCA Console Set Requesting

[Console User]

I was given recently a 1986 RCA 25 Inch Console Set . Model GLR683TR.

The picture is pretty good for it's age. It has one issue I have noticed however.

When you first turn the set on the back screen is over red in color. The picture when first coming on the screen looks somewhat blurred but adjusts out very nicely after a bit. Then shortly after the TV is on few just a few minutes the back screen becomes more of a mixture of blue and slight red color mixed in. I think this makes the blacks look a little red or purple colored on certain screen shots. Can anyone tell me if I should try to adjust the TV or just leave as is? Also, would I adjust the Bias or the Gain on the controls on back of TV? It is set pretty bright but have backed that off some already.