create polylines with different colors in leaflet

Question

I have one function which creates poly line & adds that polyline to map

function makeRoute(e)
{
    if(pointsSelection.length > 0)
    {
        pointsSelection.push(e.target.getLatLng());
        var firstpolyline = new L.Polyline(pointsSelection, {
        color: 'blue',
        weight: 5,
        smoothFactor: 1
        });

        firstpolyline.addTo(map);

        pointsArrayCollection.push(pointsSelection);
        polyArrayCollection.push(firstpolyline);

        selection = [];
        pointsSelection = [];
    }
    else
    {
        alert("Please select more than one point");
    }
}

my problem is that It adds line with same color every time.

I want to add poly lines with different colors every time.

So how can I change color of polyline dynamically.