Color CRT monitors
⦁    A CRT monitors displays color pictures by using a combination of phosphors that emit different colored light.
⦁    It produces range of colors by combining the light emitted by different phosphors.

There are two basic techniques for color display:
⦁    Beam-penetration technique
⦁    Shadow-mask technique

Beam-penetration technique
⦁    This technique is used with random scan monitors.
⦁    In this technique inside of CRT coated with two phosphor layers usually red and green. The outer layer of red and inner layer of green phosphor.
⦁    The color depends on how far the electron beam penetrates into the phosphor layer.
⦁    A beam of fast electron penetrates more and excites inner green layer while slow electron excites outer red layer.
⦁    At intermediate beam speed we can produce combination of red and green lights which emit additional two colors orange and yellow.
⦁    The beam acceleration voltage controls the speed of the electrons and hence color of pixel.
⦁    It is a low cost technique to produce color in random scan monitors.
⦁    It can display only four colors.
⦁    Quality of picture is not good compared to other techniques.
 

Shadow-mask technique

⦁    It produces wide range of colors as compared to beam-penetration technique.
⦁    This technique is generally used in raster scan displays. Including color TV.
⦁    In this technique CRT has three phosphor color dots at each pixel position. One dot for red, one for green and one for blue light. This is commonly known as Dot Triangle.
⦁    Here in CRT there are three electron guns present, one for each color dot. And a shadow mask grid just behind the phosphor coated screen.
⦁    The shadow mask grid consists of series of holes aligned with the phosphor dot pattern.
⦁    Three electron beams are deflected and focused as a group onto the shadow mask and when they pass through a hole they excite a dot triangle.
⦁    In dot triangle three phosphor dots are arranged so that each electron beam can activate only its corresponding color dot when it passes through the shadow mask.
⦁    A dot triangle when activated appears as a small dot on the screen which has color of combination of three small dots in the dot triangle.
⦁    By changing the intensity of the three electron beams we can obtain different colors in the shadow mask CRT.