Changing Tracking Color with Messages

 class Demo
 {
 protected:
   ...  
   int min_hue_;
   int max_hue_;
   int min_saturation_;

 public:

 Demo (ros::NodeHandle & nh):nh_ (nh), it_ (nh_)
 {
   ...
   hue_set_sub_ = nh_.subscribe("/hue_set", 1000, 

&Demo::hueSetCallback, this);

   min_hue_        =  6;
   max_hue_        = 26;
   min_saturation_ = 96;
 }