I just cobbled the following idea together and it seems to work out OK:
Create a text widget and make the text value ##### (or something else that activates a bunch of pixels - * might work too)
Make the color of it Red
Make the data source "Probe"
Choose the robot in the dialog, choose "controller" as the probe, choose get_info as the command,click test. Choose "uptime" from the list.
select OK to save it.
Expand the color map section of the text widget and create an entry with the value 1 and a color of green.
So what seems to happen is that the widget will display the text and color of the default non-map entry. So in my case I would get a line of red hash marks. It then immediately runs the probe callback and gets the up time value. Since that value is > 1 it paints the string of hash marks green. That's the indication my robot is up. If I then stop the robot, the next callback will generate an error and so the returned value will no longer be > 1 and so it will revert back to the default red color.
If you want the value of the returned data item in the text box use $VAR in the place where you want it.
Enjoy
-Garin