Example

function setColorValueQuantum()
{
    $image = new \Imagick();

    $quantumRange = $image->getQuantumRange();

    $draw = new \ImagickDraw();
    $color = new \ImagickPixel('blue');
    $color->setcolorValueQuantum(\Imagick::COLOR_RED, 128 * $quantumRange['quantumRangeLong'] / 256);

    $draw->setstrokewidth(1.0);
    $draw->setStrokeColor($color);
    $draw->setFillColor($color);
    $draw->rectangle(200, 200, 300, 300);

    $image->newImage(500, 500, "SteelBlue2");
    $image->setImageFormat("png");

    $image->drawImage($draw);

    header("Content-Type: image/png");
    echo $image->getImageBlob();
}