- When printing screens over screens, the printer has to be careful to avoid moiré patterns
- To achieve this, the screen angles for each color must vary by 30°. Black is always at 45°, so the other screens would have to be printed at 15°, 75° and 105°
- However, the fourth color would have the same angle as the first - which won't work
- One color screen must be out of 30° variance with the rest, so yellow is printed at 0°. (Yellow is much lighter than the other colors and the moiré it creates is less noticeable.)
