This is my code for drawing bus seat. Each `Button` represents a seat drawn in the `GridPane`. I want to change the seat color from green to yellow when someone clicks on the seat. So far I have done this. If I click on the button it prints "hellow world" in output window. But button color doesn't change in the UI. Here is my code:

```
public static GridPane drawBus(int rows, int col, String ss){
    GridPane table = new GridPane();
    table.setHgap(5);
    table.setVgap(5);
    table.setAlignment(Pos.CENTER);
    String seatName;

    if(ss.equals("ROW WISE")||ss.equals("Row Wise")||ss.equals("row wise")){
    for(int i=0; i<rows; i++){

        for(int j=0;j<col; j++)
        {
        seat=new Button();
        seat.setAlignment(Pos.CENTER);
        seat.setPrefSize(80, 31);

        seatName=numToString(i+1)+(j+1);
        seat.setText(seatName);
        seat.setStyle("-fx-background-color: MediumSeaGreen");

        seat.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {

            seat.setStyle("-fx-background-color: Yellow");
            System.out.println("Hello World!");

        }
        });

        busSeatList.put(seatName, 0);

        //add them to the GridPane
        table.add(seat, j, i); //  (child, columnIndex, rowIndex)

     }

    }
    }
    else
    {
      for(int i=0; i<rows; i++){

        for(int j=0;j<col; j++)
        {
        seat=new Button();
        seat.setAlignment(Pos.CENTER);
        seat.setPrefSize(80, 31);

        seatName=(i+1)+numToString(j+1);
        seat.setText(seatName);
        seat.setStyle("-fx-background-color: MediumSeaGreen");

        seat.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {
            System.out.println("Hello World!");
            //seat.setStyle("-fx-background-color: Yellow");

        }
        });

        busSeatList.put(seatName, 0);
        //add them to the GridPane
        table.add(seat, j, i); //  (child, columnIndex, rowIndex)

       }

    }

    }

    return table;
}

```