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": "Point",
        "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 (feature.attributes.id == 1) {
        return "red";
      } else if (feature.attributes.id == 2) {
        return "blue";
      } else if (feature.attributes.id == 3) {
        return "cyan";
      } else {
        return "yellow";
      }
    }
  };


  var yourStyle = new OpenLayers.Style({
    fillColor: "white",
    strokeColor: "${getColor}",
    strokeOpacity:...