The RSI is just an indicator and would be the Area overlay in the SamplesBrowser.  As an indicator the brushes that control color would be the .brush property and the .negativeBrush property. 

So in ObjC the code would look something like

            financialIndicator.negativeBrush = [[IGBrush alloc] initWithColor:[UIColor greenColor

                                                                               ]];

            financialIndicator.brush=[[IGBrush alloc] initWithColor:[UIColor blueColor

                                                                     ]];