labelBackgroundColor: String

Sets the Crosshair Label background color. The value of labelBackgroundColor can be a “HTML Color Name” or “hex” code.

var  chart =  new  CanvasJS.Chart("container",
{
 .
 .
 axisY:{
	crosshair: {
		enabled: true,
		labelBackgroundColor: "black",
		.
		.
	}
 },
 .
 . 
});
chart.render();