color.java

 // generates a pair of colors separated by alpha controlled by a level
    private Pair<Integer, Integer> getRandomColor(int level) {
        int red = (int)(Math.random() * 255);
        int green = (int)(Math.random() * 255);
        int blue = (int)(Math.random() * 255);

        // factor in level
        int alpha1 = 200 + (int)(Math.random() * 55);
        int delta = (10 - level) * 5;
        int alpha2 = alpha1 > 227 ? alpha1 - delta : alpha1 + delta;

        int color1 = Color.argb(alpha1, red, green, blue);
        int color2 = Color.argb(alpha2, red, green, blue);

        Pair<Integer, Integer> colorPair = new Pair(color1, color2);
        return colorPair;
    }