Abstract: A set of auxiliary deflection coils are placed on opposite sides of a multi-beam color television picture tube having a deflection yoke and color purity adjustment apparatus. The tube is operated to cause a raster to be scanned and the auxiliary coils are energized to cause the beams to be deflected from their nominal beam landing sites in predetermined direction and magnitude within each of at least two regions of the raster in order to simulate misregister caused by television receiver magnetic environment. Color purity is then adjusted in the presence of the simulated misregister.