Turtlesim: Unable to change background colour using .launch file

edit

Hello, I am trying to use .launch file to change the backgroud colour of the turtlesim node.

Here are my Codes:

First one:

    <launch>


    <node name="" pkg="turtlesim" type="turtlesim_node" output="screen" ns="/">

    <rosparam  ns="/">

    background_b: 10

    </rosparam>


    </node>
    <node name="turtle_teleop_key" pkg="turtlesim" type="turtle_teleop_key" output="screen" />

    </launch>

and the second one:

<launch>


<node name="turtlelaunch" pkg="turtlesim" type="turtlesim_node" output="screen" ns="/">
<param name ="/background_b" value="100" />
</node>
<node name="turtle_teleop_key" pkg="turtlesim" type="turtle_teleop_key" output="screen" />

</launch>

the output for rosparam_get /

nac@nac-Lenovo-G560:~/nachiket_ws/src/handouts/launch$ rosparam get /
background_b: 255
background_g: 86
background_r: 69
rosdistro: 'indigo

  '
roslaunch:
  uris: {host_nac_lenovo_g560__40475: 'http://nac-Lenovo-G560:40475/'}
rosversion: '1.11.10

  '
run_id: e57a1672-0332-11e5-87f2-ec55f98a32e6
turtlelaunch: {background_b: 100}

and the rosparam list

nac@nac-Lenovo-G560:~/nachiket_ws/src/handouts/launch$ rosparam list
/background_b
/background_g
/background_r
/rosdistro
/roslaunch/uris/host_nac_lenovo_g560__40475
/rosversion
/run_id
/turtlelaunch/background_b

I am still unable to change the background colour. Even if the global namespace is specified, a new namespace is being create and the turtlesim background paramter that is to be set is getting sent under that namespace.

What am I missing ?