How to shuffle colour balls?
public IEnumerable<Color> GetColors()
{
   int count = 400;
   // queue or another data structure to hold the last generated colors
   Queue<Color> lastColors = new Queue<Color>();
   var availableColor = new Dictionary<Color, int> {
     {Red, 100}, {Yellow, 40}, ...
   };
   Color nextColor = null;
   while(count > 0)
   {
     do {
       /* randomly pick from color buckets */
       nextColor = /* choose random color based on the weights*/;
     } while(/*it satisfies the condition, that it is not 3rd same color in a row*/)
     yield return nextColor;
     count--;
   }
}