Leaflet change circle marker color based on text field

I have circle markers on my leaflet map using the below code which all works fine.

However I want to show the markers in a different color based on the attribute field named 'stype'.

Any help or guidance on how I can achieve this?

        function siteslabels (feature, layer){
        layer.bindPopup("<p class='info header'>"+ 
        "<b>" + feature.properties.SITE + "</b>" + 
        "</br>" + feature.properties.Address1 +
        "</br>" + feature.properties.stype +
        "</p>");
        };


        var geojsonMarkerOptions = {
            radius: 8,
            fillColor: 'green',
            color: 'black',
            weight: 1,
            opacity: 1,
            fillOpacity: 0.8
        };

        L.geoJson(sites, {
            pointToLayer: function (feature, latlng) {
                return L.circleMarker(latlng, geojsonMarkerOptions);
            },
            onEachFeature: siteslabels
        }).addTo(map);