Server-Side:

 protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                Map1.MapBackground.BackgroundBrush = new GeoSolidBrush(GeoColor.FromHtml("#E5E3DF"));
                Map1.CurrentExtent = new RectangleShape(-180, 90, 180, -90);
                Map1.MapUnit = GeographyUnit.DecimalDegree;

                WorldMapKitWmsWebOverlay worldMapKitOverlay = new WorldMapKitWmsWebOverlay();
                Map1.CustomOverlays.Add(worldMapKitOverlay);
                Map1.MapTools.MouseCoordinate.Enabled = true;
                ContextMenu menuOnEventLayer = new ContextMenu("area", 200);
                ContextMenuItem menu2 = new ContextMenuItem("click me");
                menu2.OnClientClick = "changeColor";
                menuOnEventLayer.MenuItems.Add(menu2);

                Feature feature1 = new Feature(new RectangleShape(-10, 10, 0, -10)); feature1.Id = "1";
                Feature feature2 = new Feature(new RectangleShape(10, 10, 20, -10)); feature2.Id = "2";
                
                Map1.HighlightOverlay.Features.Add("multipolygon1", feature1);
                Map1.HighlightOverlay.Features.Add("multipolygon2", feature2);
                Map1.HighlightOverlay.ContextMenu = menuOnEventLayer;
            }
        }


Client-Side:

    <script type="text/javascript">
        var lastSelectedFeature;
        var layer;
        function changeColor() {
            if (lastSelectedFeature.feature.id == "1")
            { lastSelectedFeature.feature.style.fillColor = "#F3AF20"; HideContextMenus(); }
            else {
                lastSelectedFeature.feature.style.fillColor = "#F12B20"; HideContextMenus();
            }
            layer.redraw();
        }

        function OnMapCreated(map) {
            layer = map.layers[1];
            map.layers[1].events.register('featureselected', map.layers[1], function (feature) {
                lastSelectedFeature = feature;
            });
        }
    </script>