A color display system includes a color cathode ray tube having an electron gun having at least a cathode, a control electrode, an accelerating electrode, a focus electrode and an anode. The focus electrode includes a first focus electrode, a second focus electrode and a third focus electrode. The first focus electrode faces the accelerating electrode, a first quadrupole lens is formed in at least one of opposing ends of the first and second focus electrodes. A second quadrupole lens is formed in at least one of opposing ends of the second focus electrode on the third focus electrode side and a portion of the third focus electrode on the second focus electrode side, and the second quadrupole lens is formed of at least one pair of plate electrodes extending along the tube axis and facing each other across the electron beams, wherein a dynamic focus voltage varying with deflection of electron beams is applied to the first and third focus electrodes so that the first quadrupole lens produces horizontally diverging and vertically focusing actions on the electron beams and the second quadrupole lens produces horizontally focusing and vertically diverging actions on the electron beams, and a dynamic differential focus voltage Dv and a voltage Av applied to the accelerating electrode satisfy the following inequality, 0.2.ltoreq.Dv/Av.ltoreq.4.