OpenLayers Stylemap Style Context vectorlayer

HTML

<script src="http://openlayers.org/api/OpenLayers.js"></script>
<h2>OpenLayers Vector dynamic Style with context function </h2>

<div id="map"></div>

CSS

@import url(http://fonts.googleapis.com/css?family=Oswald:400, 700, 300);
 html, body {
    font-family:'Oswald', sans-serif;
    font-style: normal;
    font-weight: 400;
    font-size: 12px;
    color: #2F8CEA;
    width:100%;
    height:100%;
}
#map {
    width:97%;
    height:87%;
    border:1px solid #2F8CEA;
    margin: auto;
}

JavaScript

(function () {
    var map, layer;


    map = new OpenLayers.Map('map');
    layer = new OpenLayers.Layer.OSM("Simple OSM Map");
    map.addLayer(layer);
    map.setCenter(

    new OpenLayers.LonLat(-1.1240386962890625,
    44.68500966685889).transform(
    new OpenLayers.Projection("EPSG:4326"),
    map.getProjectionObject()), 11);


    var featurecollection = {
        "type": "FeatureCollection",
            "features": [{
            "type": "Feature",
                "properties": {
                "marker-color": "#7e7e7e",
                    "marker-size": "medium",
                    "marker-symbol": "",
                    "id": 1
            },
                "geometry": {
                "type": "markers",
                    "coordinates": [-1.1789703369140625,
                44.698677475225224]
            }
        }, {
            "type": "Feature",
                "properties": {
                "marker-color": "#7e7e7e",
                    "marker-size": "medium",
                    "marker-symbol": "",
                    "id": 2
            },
                "geometry": {
                "type": "Point",
                    "coordinates": [-1.0200119018554688,
                44.687206496456966]
            }
        }, {
            "type": "Feature",
                "properties": {
                "marker-color": "#7e7e7e",
                    "marker-size": "medium",
                    "marker-symbol": "",
                    "id": 3
            },
                "geometry": {
                "type": "Point",
                    "coordinates": [-1.251068115234375,
                44.62981752172151]
            }
        }]
    };

    var geojson_format = new OpenLayers.Format.GeoJSON({
        'internalProjection': new OpenLayers.Projection("EPSG:900913"),
            'externalProjection': new OpenLayers.Projection("EPSG:4326")
    });

    var your_context = {
        getColor: function (feature) {
            if...