Say you want to plot two TH2Ds with on the same pad but different color paletettes?

This is possible, but requires a touch of fancy ROOT-ing. Actually, it's not that much, it just takes a lot of time to figure it out. So here it is.

Fair warning, the order of all the gPad->Modified's etc seems very important to no seg fault.

In include the main (demo.cc) and the Makefile.

///////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
///////		demo.cxx
//////		Nov 2018, Brian Clark 
//////		Demonstrate how to draw 2 TH2D's with two different color palettes (needs ROOT6)
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////

//C++
#include <iostream>

//ROOT Includes
#include "TH2D.h"
#include "TCanvas.h"
#include "TStyle.h"
#include "TExec.h"
#include "TColor.h"
#include "TPaletteAxis.h"
#include "TRandom3.h"

using namespace std;

int main(int argc, char **argv)
{

	gStyle->SetOptStat(0);

	TH2D *h1 = new TH2D("h1","h1",100,-10,10,100,-10,10);
	TH2D *h2 = new TH2D("h2","h2",100,-10,10,100,-10,10);

	TRandom3 *R = new TRandom3(time(0));
	int count=0;
	while(count<10000000){
		h1->Fill(R->Gaus(-4.,1.),R->Gaus(-4.,1.));
		count++;
	}

	TRandom3 *R2 = new TRandom3(time(0)+100);
	count=0;
	while(count<10000000){
		h2->Fill(R2->Gaus(4.,1.),R2->Gaus(4.,1.));
		count++;
	}

	TCanvas *c = new TCanvas("c","c",1100,850);

	h1->Draw("colz");
		TExec *ex1 = new TExec("ex1","gStyle->SetPalette(kValentine);");
		ex1->Draw();
		h1->Draw("colz same");
	gPad->SetLogz();
	gPad->Modified();
	gPad->Update();

	TPaletteAxis *palette1 = (TPaletteAxis*)h1->GetListOfFunctions()->FindObject("palette");
	palette1->SetX1NDC(0.7);
	palette1->SetX2NDC(0.75);
	palette1->SetY1NDC(0.1);
	palette1->SetY2NDC(0.95);

	gPad->SetRightMargin(0.3);
	gPad->SetTopMargin(0.05);

	h2->Draw("same colz");
		TExec *ex2 = new TExec("ex2","gStyle->SetPalette(kCopper);"); //TColor::InvertPalette();
		ex2->Draw();
		h2->Draw("same colz");
	gPad->SetLogz();
	gPad->Modified();
	gPad->Update();

	TPaletteAxis *palette2 = (TPaletteAxis*)h2->GetListOfFunctions()->FindObject("palette");
	palette2->SetX1NDC(0.85);
	palette2->SetX2NDC(0.90);
	palette2->SetY1NDC(0.1);
	palette2->SetY2NDC(0.95);

	h1->SetTitle("");
	h1->GetXaxis()->SetTitle("X-Value");
	h1->GetYaxis()->SetTitle("Y-Value");

	h1->GetZaxis()->SetTitle("First Histogram Events");
	h2->GetZaxis()->SetTitle("Second Histogram Events");

	h1->GetYaxis()->SetTitleSize(0.05);
	h1->GetXaxis()->SetTitleSize(0.05);
	h1->GetYaxis()->SetLabelSize(0.045);
	h1->GetXaxis()->SetLabelSize(0.045);

	h1->GetZaxis()->SetTitleSize(0.045);
	h2->GetZaxis()->SetTitleSize(0.045);
	h1->GetZaxis()->SetLabelSize(0.04);
	h2->GetZaxis()->SetLabelSize(0.04);
	
	h1->GetYaxis()->SetTitleOffset(1);
	h1->GetZaxis()->SetTitleOffset(1);
	h2->GetZaxis()->SetTitleOffset(1);

	c->SetLogz();
	c->SaveAs("test.png");

}

LDFLAGS=-L${ARA_UTIL_INSTALL_DIR}/lib -L${shell root-config --libdir}
CXXFLAGS=-I${ARA_UTIL_INSTALL_DIR}/include -I${shell root-config --incdir}
LDLIBS += $(shell $(ROOTSYS)/bin/root-config --libs)