I'm a making my first android app and for part of it I need some shaded areas over a mapview. I've got this working so far but the when I set the alpha of the fill colour, it goes strange. I'm not allowed to post images yet, but you can see what happens here: http://i.imgur.com/leXmc.png

I'm not sure what causes it, but here is some code from where it gets drawn.

    public boolean draw(Canvas canvas, MapView mapView, boolean shadow,
        long when) {
    Paint paint = new Paint();
    paint.setStrokeWidth(2);
    paint.setColor(android.graphics.Color.GREEN);     
    paint.setStyle(Paint.Style.FILL_AND_STROKE);
    paint.setAlpha(25);
    screenPoints = new Point[10];
    Path path = new Path();
    for (int x = 0; x<greenZone.length; x++){
        screenPoints[x] = new Point();
        mapView.getProjection().toPixels(greenZone[x], screenPoints[x]);            
    }
    path.moveTo(screenPoints[0].x, screenPoints[0].y);
    for (int x = 1; x < screenPoints.length-1; x++){
        paint.setAlpha(25);
        if (x<9){
        path.lineTo(screenPoints[x].x, screenPoints[x].y);
        canvas.drawPath(path, paint);
        }
        else{
        path.moveTo(screenPoints[screenPoints.length-1].x, screenPoints[screenPoints.length-1].y);
        path.lineTo(screenPoints[0].x, screenPoints[0].y);
        canvas.drawPath(path, paint);               
        }       
    }

    return true;
}

Thanks.