Hex Color Code Validation Regular Expression

Hex color codes are widely used in CSS, design tools, and UI configuration files to represent colors with hexadecimal digits. This pattern validates the two most common formats: three-digit shorthand like#fff and six-digit full values like #1A2B3C. It requires the leading hash symbol and accepts uppercase or lowercase hexadecimal characters. An alpha-capable variant is also included below for interfaces that store transparency directly in the color value while still accepting the regular 3-digit and 6-digit forms.

Recommended Solution

^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$

Explanation

^# - Start of the string followed by a required #.
(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}) - Matches either exactly 3 or exactly 6 hexadecimal digits.
[0-9a-fA-F] - A single hexadecimal digit: 0-9, a-f, or A-F.
$ - End of the string.

Notes

This pattern validates format only. It does not normalize the value or convert shorthand colors like #abc into #aabbcc.
The recommended pattern intentionally excludes alpha channels. Use the alternative pattern below when you want to accept #RRGGBBAA in addition to the regular 3-digit and 6-digit forms.
If you also accept named CSS colors like red or functional formats like rgb(255, 0, 0), validate those separately rather than weakening this regex.
Hex colors commonly appear in style systems alongside token names and other configuration values.

Implementation

const hexColorRegex = /^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/;
const isValidHexColor = (color) => hexColorRegex.test(color);

import re

def is_valid_hex_color(color):
  hex_color_regex = r"^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$"
  return re.match(hex_color_regex, color) is not None

use regex::Regex;

fn is_valid_hex_color(color: &str) -> bool {
  let hex_color_regex = Regex::new("^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$")
    .expect("Could not parse hex color validation regex");
  hex_color_regex.is_match(color)
}

package main

import (
  "regexp"
)

func isValidHexColor(color string) bool {
  hexColorRegex := "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$"
  re := regexp.MustCompile(hexColorRegex)
  return re.MatchString(color)
}

import Foundation

func isValidHexColor(_ color: String) -> Bool {
  let hexColorRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$"
  return NSPredicate(format: "SELF MATCHES %@", hexColorRegex).evaluate(with: color)
}

using System;
using System.Text.RegularExpressions;

class Application {
  static bool IsValidHexColor(string color) {
    string hexColorRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$";
    return Regex.IsMatch(color, hexColorRegex);
  }
}

import java.util.regex.*;

public class Application {
  public static boolean isValidHexColor(String color) {
    String hexColorRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$";
    Pattern pattern = Pattern.compile(hexColorRegex);
    Matcher matcher = pattern.matcher(color);
    return matcher.matches();
  }
}

<?php
function isValidHexColor($color) {
  $hexColorRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$";
  return preg_match("/" . $hexColorRegex . "/", $color);
}
?>

Test Cases

Hex Color	Valid
#000
#fff
#1a2
#1A2B3C
#abcdef
#ABCDEF
#123456
123456
#12
#1234
#12345
#1234567
#GGG
#12G45F
#abcdex
#fff
#fff
(empty string)

Hex With Optional Alpha

If your system supports transparency in hex notation, use a pattern that accepts #RRGGBBAAin addition to standard #RGB and #RRGGBB values.

^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$

Explanation

^# - Start of the string followed by a required #.
(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8}) - Matches 3-digit shorthand, 6-digit full hex, or 8-digit hex with alpha.
$ - End of the string.

Note: This alternative is useful when the same input can contain standard hex colors or alpha-enabled values. It still rejects unsupported lengths such as 4-digit shorthand.

Implementation

const hexColorAlphaRegex = /^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$/;
const isValidHexColorWithAlpha = (color) => hexColorAlphaRegex.test(color);

import re

def is_valid_hex_color_with_alpha(color):
  hex_color_alpha_regex = r"^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$"
  return re.match(hex_color_alpha_regex, color) is not None

use regex::Regex;

fn is_valid_hex_color_with_alpha(color: &str) -> bool {
  let hex_color_alpha_regex = Regex::new("^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$")
    .expect("Could not parse alpha hex color validation regex");
  hex_color_alpha_regex.is_match(color)
}

package main

import (
  "regexp"
)

func isValidHexColorWithAlpha(color string) bool {
  hexColorAlphaRegex := "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$"
  re := regexp.MustCompile(hexColorAlphaRegex)
  return re.MatchString(color)
}

import Foundation

func isValidHexColorWithAlpha(_ color: String) -> Bool {
  let hexColorAlphaRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$"
  return NSPredicate(format: "SELF MATCHES %@", hexColorAlphaRegex).evaluate(with: color)
}

using System;
using System.Text.RegularExpressions;

class Application {
  static bool IsValidHexColorWithAlpha(string color) {
    string hexColorAlphaRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$";
    return Regex.IsMatch(color, hexColorAlphaRegex);
  }
}

import java.util.regex.*;

public class Application {
  public static boolean isValidHexColorWithAlpha(String color) {
    String hexColorAlphaRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$";
    Pattern pattern = Pattern.compile(hexColorAlphaRegex);
    Matcher matcher = pattern.matcher(color);
    return matcher.matches();
  }
}

<?php
function isValidHexColorWithAlpha($color) {
  $hexColorAlphaRegex = "^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$";
  return preg_match("/" . $hexColorAlphaRegex . "/", $color);
}
?>

Test Cases

Hex Color With Optional Alpha	Valid
#000
#fff
#123456
#00000000
#FFFFFFFF
#1A2B3C7F
#abcdef99
#123456FF
#12
#1234
#1234567
#123456789
#GGGGGGGG
#GGG
#12G45F99
#00000000
#00000000
(empty string)