Anyone who has ever opened Photoshop has been met with the question of using RBG or CMYK at some point. These might seem like arbitrary options at first, but each represents a different approach to creating — and displaying — colour. The distinction is explained in a new video from Express Cards RGB stands for Red, Green, Blue, because those are the three colours it uses to create every other colour in the RGB palette. Colours are added together in varying amounts to produce new ones. (Red + green = yellow, for instance.) The display you're reading these words on is almost certainly using RGB. When red, green and blue are turned up all the way, you get white.
CMYK is a little more complicated. Unlike RGB which combines colours, CMYK is subtractive, meaning white is the absence of any colour. Even the acronym, which stands for Cyan, Magenta, Yellow and Key, is more confusing. "What the hell colour is key?" you might be asking. Well, key is black, but its name points to CMYK's intended use: printed media. In old printing presses, metal plates got coated in coloured inks, and the key plate, which usually had the darkest ink on it, is what provided all the detail and contrast to the image.
In a nutshell, the difference is that RGB is additive and displays better on a screen; CMYK is subtractive and is intended for a printed page. May your images forever be colour-accurate.