This technique is used in raster scan display devices. It gives much wider range of colors than a beam penetration method. A shadow Mask CRT has three phosphor color dots at each pixel location. One phosphor dot emits a red light, another emits green light and the last one emits a blue light.
This type of CRT also has three electron guns one for each color dot.
A shadow mask grid is installed just behind the phosphor coated screen. The three electron beams are deflected and focused as a group onto the shadow mask, which contains a series of very fine holes aligned with the phosphor dot patterns.
When the three beams pass through a hole in the shadow mask, they activate a dot triangle, which appears as a small color spot on the screen .Different colors can be obtained by varying the intensity levels. More than 17 million different colors can be obtained in a full color system.