title: Color a pixel in python opencv
body: <p>I need to color a pixel in an image. I use opencv and python.<br>
  I tried <code>img[x,y]=[255 255 255]</code> to color a <code>pixel(x,y)</code> but it wont work :(   </p>
  
  <p>Is there is any mistake in this?<br>
  Can you suggest any method?</p>
  
  <p>Thanks in advance.</p>