As a designer, you're probably familiar with a few different ways of digitally selecting colors. One of the most used and straight-forward methods is the RGB-notation for example. It's easy to use as it basically works the same way as mixing the colors in real life. Most color notation methods actually work in a similar way. The difference is the way it is communicated. While the RGB-notation, using the numbers 0 to 255, is quite long, notations such as hex codes came to be used more. Hex stands for hexadecimal and uses the letters A to F, representing the numbers 10 to 15, and uses the numbers 0 to 9 to represent their decimal values. A hex color code starts with a "#"-character and is followed by six hexadecimal digits where the first two represent the color red, the two after that green and the last two represent the color blue. When you mix these three colors, you get the color that corresponds to the hex color code.
