RGB is an additive color process, meaning that 0-0-0 is a black monitor and the colors are created by adding red, green, and blue light. CMYK is a subtractive process in which 0-0-0-0 is a white surface (paper, T-shirt, etc.) where the light reflected off the white is made up of all colors and the cyan, magenta, yellow, and black ink block specific colors from reflecting. So printing (screen, digital, DTG) is done with CMYK inks, however in the digital/ DTG realm, the monitor displays the image in RGB and the colors must be interpreted to print in CMYK. Most inkjet printers are designed to accept RGB images which can be viewed on a monitor, and print them out as CMYK.