Because not all computer systems are capable of displaying 24–bit color, developers have agreed on a more limited palette of colors to be supported by all browsers. The minimum standard for Windows computers is 8–bit color, which can represent a total of 256 different colors. 216 of these have been assigned by marking each of the three primary color axes at six equal increments (6 to the 3rd power = 216). Each increment is 20% of the range of values, corresponding to 51 units (33 in hex).

Colors consisting of these values are guaranteed to be correctly displayed by all major browsers. They are easy to recognize and use because they contain only the values 00, 33, 66, 99, CC, and FF. For example, FF9933 is a bright orange, and 666666 is a dark gray.