I had the line commented by accident. OOPS.

src/Render.java

@@ -201,7 +201,7 @@ public class Render extends Canvas implements Runnable, MouseListener,
     }
 
     public void draw(int x, int y, int color) {
-        //if (_pixels[x + y * width] != color)
+        if (_pixels[x + y * width] != color)
             _pixels[x + y * width] = color;
     }