For TVs that don't have any kind of composite/component shared ports:
You can plug an old video game console's yellow composite plug into any TV's green component video slot and it will work, and come in much sharper... BUT in black and white.
Component video (red/green/blue cords) use the green channel as the main brightness (luminance) and sync channel, the other two cables carry the brightness information for the red and blue channels, which are combined to create your color picture. Composite video (the yellow cable) carries both the brightness and color information on the same line, which is why the quality isn't quite as good.
If you plug a yellow composite cable to your green component port, it will take the brightness information from composite and think it's meant to be the green channel. Since there's no information from the red or blue channels, it can only show a black and white picture.
In theory, you could get three different game consoles with yellow composite cords, plug each yellow cable into your green red and blue component ports and get a crazy colored image from all three...