For the purposes of capturing, displaying or printing the visible color spectrum, devices such as cameras, monitors, printers and software need a formula. As an example, the RGB Color Mode is named so because it calculates the color to render by blending the 3 of the the primary colors of Red Green and Blue light. RGB can render all the colors we see. So why use anything else? While light will work for cameras and monitors, it can not be used to create color for most printing. The most commonly used Color Mode for printing is the 4 channel CMYK Color Mode. Like RGB, Cyan, Magenta, Yellow and BlacK are blended together to create other colors. The 4 channels of CMYK are not needed for Rub on Transfers as transfers  are printed with single solid colors. A green transfer is printed with single solid green ink not by printing Yellow on top of Cyan to make a green color. When preparing art for Rub on Transfers, the Single Channel Color Mode Grayscale is used.