hex2rgb.php

<?php

function hex2rgb($color = '#fff')
{
    $color  = ltrim($color, '#');
    $length = strlen($color);
    
    if (preg_match('/[^0-9a-f]/i', $color) or $length <> 3 && $length <> 6) {
        throw new Exception('Invalid color format');
    }
    
    if ($length == 3) {
        $color = preg_replace('/(.)/', '$1$1', $color);
    }
    
    $color = hexdec($color);
    
    $r = 0xff & ($color >> 16);
    $g = 0xff & ($color >> 8);
    $b = 0xff & $color;
    
    return sprintf('rgb(%d, %d, %d)', $r, $g, $b);
}

echo hex2rgb('#000')    . PHP_EOL; // rgb(0, 0, 0)
echo hex2rgb('#ffffff') . PHP_EOL; // rgb(255, 255, 255)