How hexadecimal colors work

A hex color is a compact way to describe the red, green, and blue light used to display a color on a screen.

The six digits

A standard hex color contains six hexadecimal digits after a number sign: #RRGGBB. The first pair controls red, the second pair controls green, and the third pair controls blue. Each pair ranges from 00 to FF, which equals 0 through 255 in decimal notation.

#000000 contains no red, green, or blue light and appears black. #FFFFFF places every channel at full intensity and appears white. Most colors are mixtures between those extremes.

Why the alphabet appears

Hexadecimal is base 16. It uses the digits 0 through 9 and the letters A through F. A represents 10, B represents 11, and F represents 15. Two hexadecimal digits can represent 256 values, which maps neatly to an eight-bit RGB channel.

Three-digit shorthand

When both digits in every channel are identical, CSS allows shorthand. #09F expands to #0099FF. The shorthand is convenient, but it represents a much smaller set of colors than six-digit notation.

Hex and transparency

CSS also supports four- and eight-digit notation, where the final channel represents alpha transparency. For example, #00000080 is black at roughly half opacity. HexCheck currently focuses on opaque three- and six-digit colors so each URL maps to one unambiguous background color.

Hex is a notation, not a color space

A hex value typically describes sRGB values in web design. The same numeric value can appear somewhat different across displays because of calibration, brightness, ambient light, panel technology, and color-management behavior. For critical brand or print work, test on representative hardware and use managed production workflows.