Color problems when turning a CRT TV set into an oscilloscope
This kind of surgery on a CRT is not a good idea unless you know what you're doing.  There are high voltages involved, and they can really hurt or worse.  You also can't count on just disconnecting the deflection coils and using them any way you want.  Some monitors, particularly those in older TVs used the horizontal deflection coil as part of the circuit that made the high voltage.  Old TVs are amazing feats of electrical engineering in that every part did multiple things to the extent possible.  The volumes were high enough to pay for engineers cleverly reducing the circuit by pennies at a time.

Another issue you seem to have ignored is the brightness.  The individual red, green, and blue drive signals originally came from somewhere.  Without controlling these properly you don't know what beam current, and therefore what color and brightness you end up with.  It's also quite possible to burn a hole in the phosphor by leaving the beam current on while the beam is not being deflected.  That probably happens even at a small fraction of the normal beam current when the beam is being swept in a raster pattern.

Again, messing with this stuff at your apparent skill level is not a good idea. That isn't meant as a insult, but you have to know what you can do and what you can't without a good chance of getting into trouble.