TGraph and transparent color

I need to draw more than one TGraph in the same pad, as bars (with the B option), but I need to draw these graphs only with the line of the border of the bars, and not with the bar filled. With the histograms it is possible with SetFillColor(0), that set the filled color as transparent, but with the graphs it doesn’t work.
I draw the first graph with Draw(“AB”) and the others graphs with Draw(“B”).

Thank you very much.
Best regards
Andrea Bulgarelli

   c1 = new TCanvas("c1","A Simple Graph Example",200,10,700,500);
   const Int_t n = 20;
   Double_t x[n], y[n];
   for (Int_t i=0;i<n;i++) {
     x[i] = i*0.1;
     y[i] = 10*sin(x[i]+0.2);
   gr = new TGraph(n,x,y);
   gr->SetTitle("a simple graph");