Method #1:
Code:
    private static Color IntToColorWithAplphaFF(int i)
    {
        return Color.FromArgb(0xFF, Color.FromArgb(i));
    }
Method #2:
Code:
    private static Color IntToColorWithAplphaFF2(int i)
    {
        return Color.FromArgb(i | ((0xFFFFFF - i + 1)*-1));
    }