Hex Color Code (#RGB / #RRGGBB / #RRGGBBAA) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching hex color code (#rgb / #rrggbb / #rrggbbaa), ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Hex Color Code (#RGB / #RRGGBB / #RRGGBBAA)
// ReDoS-checked | RegexVault — Web & Network > Misc

define('HEX_COLOR_CODE_RGB_RRGGBB_RRGGBBAA_PATTERN', '/^#(?:[0-9a-fA-F]{8}|[0-9a-fA-F]{6}|[0-9a-fA-F]{3})$/');

function validate_hex_color_code_rgb_rrggbb_rrggbbaa(string $input): bool {
    return (bool) preg_match(HEX_COLOR_CODE_RGB_RRGGBB_RRGGBBAA_PATTERN, $input);
}

// Example
var_dump(validate_hex_color_code_rgb_rrggbb_rrggbbaa("#fff")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Misc category and has been checked for ReDoS risk. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

The alternation order matters: 8-digit first, then 6, then 3 — prevents 6-char strings from partially matching the 3-char alternative. CSS4 also supports 4-digit (#RGBA) — add [0-9a-fA-F]{4} to support it.