Below is a snippet of the code and usage guide.

PHP Function

function colourBrightness($hex, $percent)
{
    // Work out if hash given
    $hash = '';
    if (stristr($hex, '#')) {
        $hex = str_replace('#', '', $hex);
        $hash = '#';
    }
    /// HEX TO RGB
    $rgb = [hexdec(substr($hex, 0, 2)), hexdec(substr($hex, 2, 2)), hexdec(substr($hex, 4, 2))];
    //// CALCULATE
    for ($i = 0; $i < 3; $i++) {
        // See if brighter or darker
        if ($percent > 0) {
            // Lighter
            $rgb[$i] = round($rgb[$i] * $percent) + round(255 * (1 - $percent));
        } else {
            // Darker
            $positivePercent = $percent - ($percent * 2);
            $rgb[$i] = round($rgb[$i] * (1 - $positivePercent)); // round($rgb[$i] * (1-$positivePercent));
        }
        // In case rounding up causes us to go to 256
        if ($rgb[$i] > 255) {
            $rgb[$i] = 255;
        }
    }
    //// RBG to Hex
    $hex = '';
    for ($i = 0; $i < 3; $i++) {
        // Convert the decimal digit to hex
        $hexDigit = dechex($rgb[$i]);
        // Add a leading zero if necessary
        if (strlen($hexDigit) == 1) {
            $hexDigit = "0" . $hexDigit;
        }
        // Append to the hex string
        $hex .= $hexDigit;
    }
    return $hash . $hex;
}

Function Usage

You do not have to give the color with the ‘#’ in front but if you do it will still return the new hex color with the ‘#’ auto-magically.

Lighten a color

$colour = '#ae64fe';
$brightness = 0.5; // 50% brighter
$newColour = colourBrightness($colour, $brightness);

Darken a color

$colour = '#ae64fe';
$brightness = -0.5; // 50% darker
$newColour = colourBrightness($colour, $brightness);