如何获得一定数量的随机颜色来填充网格-C#

我有一个7种颜色的列表：红色、蓝色、绿色、栗色、棕色、浅绿色和黑色。

在我的程序中，我有它，所以你点击一个框，然后这个框就会充满一种颜色。我希望每个盒子都是随机的颜色（从我的7种颜色列表中），我已经做到了以下几点：

    Random random = new Random();
        int randomColour = random.Next(0,6);
        if (e.Button == MouseButtons.Left)
        {
            //got the y values of the grid
            //got the x values of the grid
            //Randomize The Colours
            if (randomColour == 0)
            {
                Form.GetTile(x, y).FrontColour = Color.Red;
                Score = Score + 1;
            }
            else if (randomColour == 1)
            {
                Form.GetTile(x, y).FrontColour = Color.Blue;
                Score = Score + 2;
            }
            else if (randomColour == 2)
            {
                Form.GetTile(x, y).FrontColour = Color.Maroon;
                Score = Score + 5;
            }
            else if (randomColour == 3)
            {
                Form.GetTile(x, y).FrontColour = Color.Aqua;
                Score = Score + 10;
            }
            else if (randomColour == 4)
            {
                Form.GetTile(x, y).FrontColour = Color.Black;
                Score = Score - 3;
            }
            else if (randomColour == 5)
            {
                Form.GetTile(x, y).FrontColour = Color.Brown;
                Score = Score - 1;
            }
            else if (randomColour == 6)
            {
                Form.GetTile(x, y).FrontColour = Color.Green;
                Score = Score + 3;
            }

但是，我想设置我的代码，这样最多只能有20个红色框、20个蓝色框、5个绿色框、5个中棕色框、4个浅绿色框、五个栗色框和5个黑色框。

这应该是输出，除了更多的混洗。

Form.GetTile（x，y）.FrontColor是我正在从另一个类访问的属性，它会更改方框的颜色

public class ShuffledChoices<T>{
   private readonly List<T> Choices;
   private Random rng = new Random();
   public ShuffledChoices(IEnumerable<T> choices){
     Choices = new List<T>(choices);
   }
   public T PickNext(){
     var i = rng.Next(Choices.Count); // lock may not be a bad idea
     var pick = Choices[i];
     Choices.RemoveAt(i);
     return i;
   }
}

var baseChoices = Enumerable.Repeat(Colors.Red, 20)
  .Union(Enumerable.Repeat(Colors.Blue, 20))
  .Union(Enumerable.Repeat(Colors.Green, 5))...;
var shuffledColors = new SuffledChoices<Color>(baseChoices);
...
if (e.Button == MouseButtons.Left){
   Form.GetTile(x, y).FrontColour = shuffledColors.PickNext();
}

Dictionary<string, int> dictionary = new Dictionary<string, int>();
dictionary.Add("Red", 20);
dictionary.Add("Blue", 20);
dictionary.Add("Green", 5);

bool colourSelected = false;
    do
    {
        var rnd = new Random();
        var randomEntry = dictionary.ElementAt(rnd.Next(0, dictionary.Count));
        String randomKey = randomEntry.Key;
        String randomValue = randomEntry.Value;
        if(randomvalue > 0)
        {
            // Take color
            // could also add in logic to remove a color once it reaches 0, 
            // this way we don't select colors that are unavailable 
            dictionary[randomKey] = randomValue - 1;
            colourSelected = true;
        }
    }
    while(colourSelected == false);