Create new transparent color in photoshop scripting

Question

I'm trying to obtain a transparent color as background for an image with photoshop JSX scripts. The thing is that I can only create a new SolidColor(), and it won't accept 8 characters HEX colors that manage transparency...

    var bgColorHex = new SolidColor();
    bgColorHex.rgb.hexValue = options.bgColor;
    app.backgroundColor = bgColorHex;

    // ...

    app.activeDocument.selection.fill(bgColorHex);

Here I'd like to just use the fill function to fill with a transparent color instead of a solid color.

I can't find my way though their API, and the script I'm starting from is old and not maintained anymore.