The problem you're describing is called a "purity error", where the colours become mixed up due to an offset of the magnetic field on the CRT. This effects the tradjectory of the beams and so what was supposed to be red comes out as blue and so on.
Inside the monitor itself you've got a "deagussing" circuit which basically neutralises any unwanted magnetic field surrounding the CRT. If this circuit is not functioning correctly, you can end up with a purity error. You can also end up with a permanent purity error if the CRT has been damaged due to the monitor being dropped. Some monitors have a manual degauss function which you can initiate while it's switched on. If yours has that option, try setting it off while you've got the monitor on and see if the purity error clears. If not you've either got a faulty CRT, or the degauss circuit is not functioning properly, either due to dry joints somewhere or a faulty positor.
If the purity error cleared when you asked the monitor to degauss, the problem was most likely caused by you sitting the speakers too near the monitor.
Brian