title: How to put in color a certain part of the background in a plot with matlab?
body: <p>I would like to draw in grey color a certain part of the background in a plot.
  I know how to change the background color of the whole plot.I used this code 
  after the plot function:</p>
  
  <p>HANDLE = gca</p>
  
  <p>get( HANDLE );</p>
  
  <p>set( HANDLE, 'Color', [0.7,0.7,0.7] )</p>
  
  <p>Exemple: y=x^2</p>
  
  <p>How can I do to draw the blue part of the background in grey and to leave the other parts in white?
  <img src="https://i.stack.imgur.com/ATOa6.jpg" alt="enter image description here"></p>
  
  <p>Thank you in advance</p>