static string getRandomColor()
{
    Random random = new Random();

    int firstRandomColor = 0;
    int secondRandomColor = 0;
    int thirdRandomColor = 0;

    firstRandomColor = random.Next(0, 255);
    secondRandomColor = random.Next(0, 255);
    thirdRandomColor = random.Next(0, 255);

    string rgba = "";
    rgba = "'rgba(" + firstRandomColor + "," + secondRandomColor + "," + thirdRandomColor + ",0.7)'";
    return rgba;
}

string randomColor1 = getRandomColor();
    string randomColor2 = getRandomColor();
    string randomColor3 = getRandomColor();