Fill TBox

I have some TBoxes to fill with a color proportional to a number. Every Box has a different number. Now I’m using the default palette. Can I modify the palette for example with the palette used by TGraph2D? The problem is: if I modify the palette then the other objects that use the palette (like TPad) change their colors?

Here is an example showing how to modify a palette. It sets gray levels.

   TF2 *f2 = new TF2("f2","0.1+1000*((1-(x-2)*(x-2))*(1-(y-2)*(y-2)))",1,3,1,3);   
   Int_t ncol = 50;
   Int_t colors[ncol];
   TColor *col;
   Double_t dg=1/(Double_t)ncol;
   Double_t grey=0;
   for (Int_t i=0; i<ncol; i++) {
      colors[i]= i+100;
      col = gROOT->GetColor(colors[i]);
      col->SetRGB(grey, grey, grey);
      grey = grey+dg;
   f2->Draw("cont4 z");

You do not necessarely need to use TPalette. You can use colors outside a TPalette. Just make sure, like in this example, that the color indeces you modify are in a range where they will not touch the standard colors.