CMYK is a four-colour mode that utilises the colours cyan, magenta, yellow and black in various amounts to create all of the necessary colours when printing images. It is a subtractive process, meaning each additional unique colour requires light that is removed or absorbed, to create colours. When the first three colours are added together, the result is not pure black, but rather a very dark brown. The K colour, or black, is used to completely remove light from the printed picture, which is why the eye perceives the colour as black.
RGB is the colour scheme that is most often associated with electronic displays, such as LCD monitors, digital cameras and scanners. Contrary to the CMYK method, RGB is an additive type of colour mode that shines light through combinations of the primary colours, red, green and blue, in varying levels, to create a variety of different colours. When all three colours are combined and displayed to their full extent, the result is a pure white. When all three colours are combined to the lowest degree, or value, the result is black.
Printed CMYK dots. Illuminated RGB lights.