Flutter GoogleMaps - dynamic colouring of Custom Markers

Flutter Google Maps allows the use of the standard/default Marker to be used on the map. You can also apply a colour to this marker programatically to add a variety of colours to your app.

However, what I can't seem to do is use this same technique to dynamically apply a colour to a custom (white) marker. Rather than make 10 custom markers with different colours I would prefer to have a plain white one, and dynamically colour it with a Hue or colour blend.

Default Marker

    bool bToggle = true; 

    _markers.add(Marker(
        markerId: MarkerId(markerid),
        position: newPos,
        onTap: () {
          ...
        },
        infoWindow: InfoWindow(
          ...
        ),
        icon: BitmapDescriptor.defaultMarkerWithHue(
           (bToggle) ? BitmapDescriptor.hueYellow : BitmapDescriptor.hueRed
        ),        
      ));

Custom Marker

    _markers.add(Marker(
        markerId: MarkerId(markerid),
        position: newPos,
        onTap: () {
          ...
        },
        infoWindow: InfoWindow(
          ...
        ),
        icon: BitmapDescriptor.fromAssetImage(ImageConfiguration(devicePixelRatio: 2.5), 'assets/markers/pin-blue.png')
        ),        
      ));

Many thanks