Each pixel on a television screen is made up of three tiny subpixels, one red, one green, and one blue. By changing the intensity of each subpixel, a television can create any color it needs to display. The more intense a subpixel is, the brighter it is. For example, to create the color yellow, a television would turn on the red and green subpixels and turn off the blue subpixel. To create the color blue, a television would turn on the blue subpixel and turn off the red and green subpixels.
By combining different intensities of red, green, and blue light, televisions can create all the colors of the rainbow. This is also the same way that computers display colors.