The red circuitry is driven pretty hard, so that's usually the first to go (as in heavymetal4god's case). An abrupt loss of a color is usually indicative of a circuit problem; a gradual degradation is generally indicative of crt senescence. In your case the crt is likely fine (out-and-out crt failures are rare, in any event).

How well-equipped a home lab do you have? Access to an oscilloscope would be best, but a determined soul could make do with a good voltmeter...

If you are serious about troubleshooting, post back, and folks here can walk you through a procedure.