GraphicsMagick for node.js : Naturally overlay color on greyscale PNG with alpha

I am trying to colorize an image by overlaying a color on a greyscale PNG image.

The greyscale PNG is product picture with alpha channel and i want to naturally colorize this image.

I manage to apply the color to non transparent pixels but the color is composition mode is not "Over" (Photoshop = overlay).

This is the code i use to apply the color for now :

gm('product.png')
    .options({imageMagick: true})
    .fill('#ff5400')
    .colorize(100)
    .write('product_colorized.png', function (err) {
        if (!err) console.log('Image creation done');
    });

I already tried all possible options like .compose('Over'), .channel('Opacity')...etc

Does anyone has on clue on this ?