six (6) digit color codes for use use in graphic design
Hexadecimal color codes are utilized by designers to specify particular colors when coding a website file, such as the webpage you are looking at right now. This base-16 system uses the numbers 0-9 and letters A-F to create over 16,000,000 different combinations.
At one time website designers were forced to limit their choices to 216 web-safe colors in order to guarantee that all viewers, no matter how old their computer, would be able to view the color scheme properly. This is no longer relevant, as modern computers and devices display all available colors.