BlueJ - Generating Multicoloured Brick Wall

I'm trying to generate a multicoloured brick wall as part of an assignment using BlueJ.

According to the instructions we've been given, once the wall is set up and we invoke the draw() method, if we invoke the toggleMultiColoured method the bricks will go from being all read to a mix of 6 different colours...

...When I invoke the toggleMultiColoured method, however, the wall I generate is still red.

Here's the source code for the BrickWall class I wrote:

Java Code:

public class BrickWall
{
private int bWidth;
private int bHeight;
private int numRows;
private int rowLength;
private ArrayList<String> colors;
private ArrayList<Rectangle> bricks;

[Code] .....