Create fill layer white/black depending on general colour

Is there a way to write a script that will create a new fill layer dependant on the colour of the image placed in the file?

So if the image is mainly white, create a grey fill layer, or mostly black, create a white fill layer? Or is there a way to allow the user to pick the colour of the fill layer?

I currently have this as part of my script but was wondering if it could be more adaptive.

    function createFill() {
        var fillColor = new SolidColor();
        fillColor.rgb.red = 255;
        fillColor.rgb.green = 255;
        fillColor.rgb.blue = 255;
        var newLayer = doc.artLayers.add();
        newLayer.name = "fill " + (i + 1);
        doc.selection.fill(fillColor);
        newLayer.move(newLayer, ElementPlacement.PLACEAFTER);
        var fillLayer = doc.activeLayer;  
        fillLayer.move(doc.layers[doc.layers.length-1], ElementPlacement.PLACEAFTER);
    }