When I took this course, the ratio of color vs black and white content broadcasts was pretty much the same as today. In fact, with the popularity of Turner Classic Movies and other nostalgic broadcasts, there is more black and white content being broadcast today. The technology for broadcasting in color existed in the 1920s. But, most of the content for early TV came from old black and white movies, cartoons and "short subjects," like "The Little Rascals." etc. Black and white episodic TV was cheap to produce, thus profitable.
Commercial color TV came on the scene with NBC in the mid-1950's. Early broadcasts were Sporting Events, Holiday Specials and high rated shows like "Bonanza." The last network to "colorize," was CBS who spent years trying to convince the FCC to accept their patented color technology over NBCs, as the standard for the industry. If you are a fan of old TV, this explains why CBS shows were black and white about 10-years longer than NBC's.