Pedantic note on NTSC: the signal has a luma (brightness) and chroma (color) component. The NTSC standard had a place for chroma information from the get-go but it was unused for a long time. Color cameras were expensive, storage more complex, and the televisions themselves more complex and expensive. As technology improved it became more practical and broadcasters started doing color broadcasts. Old black and white televisions worked as before but then new color ones...had color. Huzzah for forward thinking specifications.

Black and white televisions just displayed the luma component of the signal. The luma component was not just the "red" signal but a measure of total brightness.