> they are physically positioned so that the holes in the shadow mask or the gaps in the aperture grille block the beams from hitting the unwanted color phospho

> they are physically positioned so that the holes in the shadow mask or the gaps in the aperture grille block the beams from hitting the unwanted color phosphors and only hit the phosphor that each beam should light up. Moreover, if you physically rotate the display, then the colour changes because that alignment is thrown off—by Earth’s magnetic field, IIRC.