TGraph *graph = new TGraph(); graph->SetMarkerColor(kRed);
TGraphErrors *graph = new TGraphErrors(n, x, y, ex, ey); graph->SetMarkerColor(kBlue);
TMultiGraph *multiGraph = new TMultiGraph(); TGraph *graph1 = new TGraph(); TGraph *graph2 = new TGraph(); graph1->SetMarkerColor(kGreen); graph2->SetMarkerColor(kMagenta); multiGraph->Add(graph1); multiGraph->Add(graph2); multiGraph->Draw("AP");This code creates a multi-graph with two graphs, and sets the marker color to green for graph1 and magenta for graph2. The graphs are then added to the multi-graph and drawn with the "AP" option. In summary, the TGraph SetMarkerColor method is used to change the colors of markers in graphs, and it is part of the ROOT library, which is widely used in high-energy physics research.