src/Drupal/Component/Utility/Color.php
public static function validateHex($hex) {
    // Must be a string.
    $valid = is_string($hex);
    // Hash prefix is optional.
    $hex = ltrim($hex, '#');
    // Must be either RGB or RRGGBB.
    $length = Unicode::strlen($hex);
    $valid = $valid && ($length === 3 || $length === 6);
    // Must be a valid hex value.
    $valid = $valid && ctype_xdigit($hex);
    return $valid;
  }
public static function validateHex($hex) {
    // Must be a string.
    $valid = is_string($hex);
    // Hash prefix is optional.
    $hex = ltrim($hex, '#');
    // Must be either RGB or RRGGBB.
    $length = Unicode::strlen($hex);
    $valid = $valid && ($length === 3 || $length === 6);
    // Must be a valid hex value.
    $valid = $valid && ctype_xdigit($hex);
    return $valid;
  }
public static function validateHex ( $ hex ) { // Must be a string. $ valid = is_string ( $ hex ) ; // Hash prefix is optional. $ hex = ltrim ( $ hex , '#' ) ; // Must be either RGB or RRGGBB. $ length = Unicode :: strlen ( $ hex ) ; $ valid = $ valid && ( $ length === 3 || $ length === 6 ) ; // Must be a valid hex value. $ valid = $ valid && ctype_xdigit ( $ hex ) ; return $ valid ; }
Validates whether a hexadecimal color value is syntactically correct.

@param $hex
The hexadecimal string to validate. May contain a leading '#'. May use
the shorthand notation (e.g., '123' for '112233').

@return bool
TRUE if $hex is valid or FALSE if it is not.
Validates whether a hexadecimal color value is syntactically correct .