NotTaR of Television Sets : Color TV only displays one color        
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Color TV only displays one color

I assume that now you have no other colors at all - no picture and no raster. Let us say it is red - R.

It is probably not the CRT. Do you have a scope? Check for the R, G, and B video signals at the CRT. You will probably find no signals for the defective colors.

This is almost certainly a chroma circuit problem as any failure of the CRT or a video driver would cause it to lose a single color - the other two would be ok. Therefore, it is probably NOT the CRT or a driver on the little board on the neck of the CRT.

Try turning up the SCREEN control to see if you can get a G and B raster just to confirm that the CRT is ok.

Locate the video drive from the mainboard for the good and a bad color. Interchange them and see if the problem moves. If so, then there is a video signal problem. If not, it is on the little CRT board.

It could be a defective chroma IC or something else in the chroma decoder.