Why is Imagick coloring an image the wrong color, and how can I overcome this?

Question

PHP

The simplest code:

$image = new Imagick();
$image->newImage(500, 500, new ImagickPixel('#fff000'));
$image->setImageFormat('png');
header('Content-type: image/png');
echo $image;

And a square should be drawn with the color #fff000 . But for some reason, the color of the displayed square is #fff100 , i.e. channel g from f0 becomes f1 . What is this nonsense? Why and how to overcome?