LIMITATIONS OF THE NTSC SYSTEM
The NTSC system is sensitive to transmission path differences which introduce phase errors that results in colour changes in the picture.
At the transmitter, phase changes in the chroma signal take place when changeover between programmes of local and television network systems takes place and when video tape recorders are switched on.
The chroma phase angle is also effected by the level of the signal while passing through various circuits. In addition crosstalk between demodulator outputs at the receiver causes colour distortion.
All this requires the use of an automatic tint control (ATC) circuit with provision of a manually operated tint control.