There are normally two sets of adjustments -- Screen and Drive. Broadly
speaking, the Screen control adjust the darkest areas of the picture, the
Drive the brightest. (There is usually no red Drive control, because the red
phosphors are/were the least-efficient, and were run "at full blast".

Looking at a monochrome image (play "Casablanca"), you need to adjust these
controls to get a neutral (colorless) image.

Try Googling "gray-scale tracking" + "crt".