Why would you have one? Want the image to look blurrier on purpose? Color TVs have one to block the color dots.
However, this practice was not universal, and archivists have now recreated colour copies (https://en.wikipedia.org/wiki/Colour_recovery) of some shows where only black and white recordings survived by reconstructing the colour from these interference signals.
As an aside, you can do all this digitally now with phenomenally sharp results.