This link will fill in the blanks: (In fact I see I'm spreading bad info above-- the screen doesn't separate
red, green, and blue-- it separates groups
of red, green, and blue phosphors. Sorry!)
How Colour TV Works
When a color TV needs to create a red dot, it fires the red beam at the red phosphor. Similarly for green and blue dots. To create a white dot, red, green and blue beams are fired simultaneously -- the three colors mix together to create white. To create a black dot, all three beams are turned off as they scan past the dot. All other colors on a TV screen are combinations of red, green and blue.
A color TV signal starts off looking just like a black-and-white signal. An extra chrominance signal is added by superimposing a 3.579545 MHz sine wave onto the standard black-and-white signal. Right after the horizontal sync pulse, eight cycles of a 3.579545 MHz sine wave are added as a color burst. Following these eight cycles, a phase shift in the chrominance signal indicates the color to display. The amplitude of the signal determines the saturation.
Depending on the polarity of the affected area's magnetic field, the electron stream is pulled off its intended target. Say the green channel is always the bottom pixel of each group of three, and the stream is being forced down, so that even if the colour guns are aiming for the red or blue, they hit the green.