In its most basic form, a color broadcast can be created by broadcasting three monochrome images, one each in the three colors of red, green, and blue (RGB). When displayed together or in rapid succession, these images will blend together to produce a full-color image as seen by the viewer. To do so without making the images flicker, the refresh time of all three images put together would have to be above the critical limit, and generally the same as a single black and white image. This would require three times the number of images to be sent in the same time, and thus greatly increase the amount of radio bandwidth required to send the complete signal and thus similarly increase the required radio spectrum. Early plans for color television in the United States included a move from very high frequency (VHF) to ultra high frequency (UHF) to open up additional spectrum.