A hex code is a way of writing an exact colour as a hash sign followed by six characters, such as #FFFFFF for white or #000000 for black. It is the most common colour format in web design, so when a designer or brand guide says "our blue is #1A73E8", any website or design tool can reproduce precisely that shade.
How to read the six characters
"Hex" is short for hexadecimal, a counting system with sixteen digits: 0 to 9, then A to F. The six characters are three pairs, one each for red, green and blue: #RRGGBB. Each pair runs from 00 (none of that colour) to FF (the maximum, equal to 255 in normal numbers). So a hex code is just a compact way to write an RGB value.
#FF0000is full red, no green, no blue: pure red.#808080is equal medium amounts of all three: grey.#1A73E8is a little red, some green and a lot of blue.
With 256 levels per channel, six-digit hex can describe 16,777,216 colours. Letters are not case-sensitive, so #1a73e8 is the same colour.
Short and long variants
CSS accepts a three-digit shorthand where each digit is doubled: #F60 means #FF6600. It also accepts eight digits, where the last pair is transparency: #00000080 is black at about 50 percent opacity.
Example: matching a shop sign
A florist wants the website to match her painted sign. She photographs it, uses an eyedropper in a design tool to sample the colour, and gets #2E5E4E. That code goes into the site's CSS, her email signature and the print shop's order, so the green is consistent everywhere. Printers will convert it to CMYK, so a printed proof is still worth checking.
Where hex codes trip people up
- Confusing O with 0. The letter O is not a hex digit;
#0O0000is invalid. - Dropping the hash in CSS.
color: 1A73E8does nothing; it needs the # sign. - Sampling from a compressed image. JPEG artefacts shift colours slightly. Get the official value from the logo file or brand guide.
- Judging contrast by eye. Run text and background hex codes through a contrast checker before publishing.
Related terms
- RGB: the colour model a hex code encodes.
- Color palette: a set of colours usually listed as hex codes.
- CSS: the language where hex codes are applied.
- Brand guidelines: where official hex values are recorded.