One color is too weak or too strong

If the problem is slight and/or has gradually gotten worse, this may just
require an adjustment of the color brightness/background/bias and/or color
gain/drive controls inside the monitor. See the section: "Brightness and color balance adjustment

Even if it appears as though there is an excess, this may actually be a
reduction in one of the primary colors. For example, a magenta tinge is
represents a reduction in the strength of the green signal.

* Too high an intensity for one of the color channels will result in a tint of
one of the primaries: red, green or blue.

* Too low an intensity for one of the color channels will result in a tint of
the complement of one of the primaries: yellow, cyan, or magenta.

* Problems mainly in the shadows or dark areas of the picture usually represent
a fault with brightness/bias/background.

* Problems mainly in the highlights or bright areas of the picture usually
represent a fault with the gain/drive.

A color that that is now suddenly brighter or darker than normal resulting in
incorrect color balance or a tint in the background could be due to a number
of causes:

* Bad cable or pin bent on cable connector.

* Bad connections or bad component in video amplifier or on CRT neck board for
that color.

* Weak gun in CRT (reduced color).

* Bad video card or incorrect software color map settings.

* For monitors with sync-on-green capability, the monitor may think you are
using sync-on-green when in fact you have separate sync. In particular,
this may result in a problem with excessive green:

(From: Bob Myers (myers@fc.hp.com)).

Some monitors provide a user-selectable setup option for "sync-on-green"
vs. separate syncs. Sometimes, this doesn't really change where the
sync itself is coming from. In those cases, it's automatically detected
but *does* change where the reference level for the video is expected
to be. You might try checking this setting, if you have it, and changing
it back and forth to check the effect. It's not likely to be the problem
in a separate-sync system like a PC, but weirder things have happened
and it's easy and cheap to check out.