In the ‘80s, X system programmers had the option to identify colors the way many developers do today: with a hexadecimal value (AKA hex value, e.g., #FFFF00) or an RGB color code (e.g., 255,255,0).

by using CSS that specifies the appearance of documents written in HTML or XML. You need a color name to specify a color, but it's a hassle to look up the names of 147 different colors.