Abstract: An improved color picture tube (10) has a shadow mask (24) mounted therein in spaced relation to a viewing screen (22) thereof. The mask has a rectangular periphery with two long sides and two short sides. A major axis (X) passes through the center of the mask and parallels the long sides thereof, and a minor axis (Y) passes through the center of the mask and parallels the short sides thereof. The mask has an aperture array (35) that includes slit-shaped apertures (36) aligned in columns (37) that essentially parallel the minor axis and end at a border of the aperture array. The improvement comprises the column-to-column spacing (aH) parallel to the major axis including a pseudo-cyclic variation at least in a portion of the mask, wherein a complete cycle within the pseudo-cyclic variation occurs in the column-to-column spacings between no more than nine consecutive columns.