The relatively small amount of network color programming, combined with the high cost of color television sets, meant that as late as 1964 only 3.1 percent of television households in the U.S. had a color set. However, by the mid-1960s the subject of color programming turned into a ratings war. A 1965 American Research Bureau (ARB) study that proposed an emerging trend in color television set sales convinced NBC that a full shift to color would gain a ratings advantage over its two competitors. As a result, NBC provided the catalyst for rapid color expansion by announcing that its prime time schedule for fall 1965 would be almost entirely in color. ABC and CBS followed suit and over half of their combined prime-time programming also moved to color that season, but they were still reluctant to telecast all their programming in color due to production costs. All three broadcast networks were airing full color prime time schedules by the 1966–67 broadcast season, and ABC aired its last new black-and-white daytime programming in December 1967. Public broadcasting networks like NET, however, did not use color for a majority of their programming until 1968. The number of color television sets sold in the U.S. did not exceed black-and-white sales until 1972, which was also the first year that more than fifty percent of television households in the U.S. had a color set. This was also the year that "in color" notices before color television programs ended, due to the rise in color television set sales, and color programming having become the norm.