Thanks for your comments but unfortunately coloring the borders was not an option, as this idea was already rejected since it was having visual problem for the end-users.

How ever since the category 4 and 5 was static, I was able to handle this by adding strip lines across the x-axis, this made the color of in the back of category 4 and 5 appear shaded.

But I am still not able to get how to handle this scenario if the values in the x-axis is dynamically.