sample

  var random;
     var result;
     random = Math.random(0, 1)
     if ( random < 0.5){
         result = (1);

     }
     else if ( random > 0.95){
         result = (2);

     }
     else{
         result = (3);

     }
     switch(result){
         case 1: document.write("<h1 class = TextRed> Красное </h1> "  ); break;
         case 2: document.write("<h1 class = TextGreen>  Зелёное </h1> " ); break;
         case 3: document.write("<h1 class = TextBlack> Чёрное </h1>" ); break;
     }