VIX background color problem

[shaeffer]

Hope everyone had a great holiday!

I am trying to simply set the background color in a daily plot of the $VIX to red when the VIX is rising and green when falling. I am doing something wrong as the background color does not change at many of the peaks and troughs.

Any help would be appreciated
Thanks
Shaeffer

function preMain(){
    setPriceStudy(false);
    setStudyTitle("VIX-UD-BG");
    setShowCursorLabel(false);
    setShowTitleParameters( false );
    setDefaultBarBgColor( Color.black); 
    
    setDefaultBarFgColor(Color.RGB(204,153,255),0);  // Purple
    setPlotType( PLOTTYPE_LINE,0);
    setDefaultBarThickness(2,0);
    
}
var xVIX  = null;
//var xVIXO  = null;
var bInit = false;

function main() {

var vVIX;
var vVIX1;

    if(bInit == false){
        xVIX   = close(sym("$VIX"));
        //xVIXO  = open(sym("$VIX"));
        bInit  = true;
    }
 
    vVIX   = xVIX.getValue(0);
    //vVIXO  = xVIXO.getValue(0);
    vVIX1  = xVIX.getValue(-1);

//   Close to previous Close relationship       
    if (vVIX > vVIX1){                // VIX rising (more fear)
        setBarBgColor(Color.maroon);  // market s/b falling
    }else if (vVIX < vVIX1){            // VIX falling (less fear)
        setBarBgColor(Color.green);     // market s/b rising
    }else{
        setBarBgColor(Color.blue);
    } 

return (vVIX);
}