In reply to puneet.

If you want to change the color of the tall shaded areas, you need to create a separate series for each color. That is, the data for each color would have to be placed in a separate column in the spreadsheet, and you would have to add each column to the chart separately and then change the color manually.

Another way would be to copy the chart into a graphic design program like Adobe Illustrator or Inkscape. You could just edit the color manually.

Finally, if it's too complicated to try to get Excel to do this for you, you could just skip Excel entirely and add the color regions manually. You could use Illustrator or Inkscape, or maybe even just PowerPoint, to draw rectangles and place them behind the chart in the correct position and with the correct width. It is not as easy to be precise, but it might save time.