The switch from black and white to color was a major step toward realistic visuals. Just as with TV itself, a mechanical method for generating color was developed first. It involved a red, blue and green wheel spinning in front of the cathode ray tube that beamed images to the screen. Then, a more complicated but better electronic method was introduced. With black-and-white, variations in voltage affected how much light was beamed to each part of the screen, basically painting an image onto the screen with light. With color, this was still true, but instead of one beam of electrons there were three, each hitting either a red, blue or green spot at each point on the screen. These color spots were used to paint the picture. Standards for color analog TV transmission were set by the NTSC in 1953.
As with every jump in technology, early color TVs were extremely expensive (over $7000 in today's dollars). To play both black-and-white and color broadcasts required two sets of circuits. There also weren't many compatible broadcasts early on, but by the late 1960s, most shows were broadcast in color. Many people waited to adopt color TVs until their favorite shows were offered in the format. By the early 1970s, color TVs were owned by about half of U.S. homes.
Now cathode ray tubes have been replaced by alternate methods of getting light and color to the screen. Liquid crystal displays (LCD) use electrical charges to change the opacity of liquid in the screen to affect shade, and backlighting passed through colored filters produces color. LED TVs are LCDs that use light emitting diodes to light the screen. Plasma TVs produce light and color by electrifying gases between plates of glass. All use different methods to get the light and color onto the screen, but the general principle of drawing the image to the screen with colored dots is the same.