x of the bin (i,j).
     <br>
     This function should be used after an histogram has been plotted with the
     option COL or COLZ like in the following example:
     <pre>
       h2->Draw("COLZ");
       gPad->Update();
       TPaletteAxis *palette =
          (TPaletteAxis*)h2->GetListOfFunctions()->FindObject("palette");
       Int_t ci = palette->GetBinColor(20,15);
     </pre>
     Then it is possible to retrieve the RGB components in the following way:
     <pre>
       TColor *c = gROOT->GetColor(c