Abstract: The present invention provides an improvement in a color display system. The system includes a cathode-ray tube having an electron gun for generating and directing three electron beams along paths toward a screen of the tube. The gun includes electrodes comprising a beam forming region, electrodes for forming a prefocus lens and electrodes for forming a main focusing lens. The system also includes a magnetic field deflection yoke. The improvement comprises means for applying a dynamic signal to one of the electrodes forming the prefocus lens when electron beam current drops below a predetermined level. The dynamic signal is a maximum voltage when there is no deflection of the electron beams and decreases in voltage to a minimum at maximum horizontal deflection of the electron beams.