void DumpColors()
{

  std::string files[4] = {"my_output_4Cores_60kEvents.root",
                          "my_output_4Cores_6kEvents.root",
                          "my_output_AllCores_60kEvents.root",
                          "my_output_AllCores_6kEvents.root" };

  for (auto fn : files) {
    cout << "Processing ..." << fn << endl;
    TFile *f = TFile::Open(fn.c_str());
    if (f) {
      TList *keys = f->GetListOfKeys();
      TIter nxk(keys);
      TKey *k = 0;
      while ((k = (TKey *)nxk())) {
        TH1F *h = dynamic_cast<TH1F*>(f->Get(k->GetName()));
        if (h) {
	  cout << k->GetName() << ": fill color is: " << h->GetFillColor() << endl;
        } else {
          cout << k->GetName() << ": not a TH1F" << endl;
        }
      }
      delete f;
    }
  }

}