asp.net mvc use angularjs post json type to controller insert database

I have a problem code. like this

View

 <div ng-app="MyPct4" ng-controller="ajaxCtrl">
    <div>
        <table>
            <tr>
                <td><b>pls input Color</b></td>
                <td><input type="text" ng-model="InputColor" /></td>
            </tr>
        </table>
        <input type="button" value="save" ng-click="AddUpdateColor()" />
    </div>
</div>

Angularjs controller

var ptc4 = angular.module("MyPct4", []);
ptc4.controller('ajaxCtrl', function ($scope, myService) {
    $scope.AddUpdateColor = function () {
                var newColor = { Color: $scope.InputColor };
                var getData = myService.AddColor(newColor);
                getData.then(function (msg) {
                    alert(msg.data);
                }, function () {
                    alert("error")
                });
            }
}

Angularjs service

ptc4.service("myService", function ($http) {
this.AddColor = function (newColor) {
                var response = $http({
                    method: "post",
                    url: "/Practice/AddColor",
                    data: JSON.stringify(newColor),
                    dataType: "json"
                });
                return response;
            }
}

MVC controller

 private TestDBEntities2 db = new TestDBEntities2();
    public string AddColor(ColorDB color)
        {
            if (color != null)
            {
                    db.ColorDB.Add(color);
                    db.SaveChanges();
                    return "add success";
            }
            else
            {
                return "add fail";
            }
        }

The result is always show alert add fail. Seems to be json can't post to MVC controller. Please help thank you so much.

ColorDB

 public partial class ColorDB
{
    public int Id { get; set; }
    public string Color { get; set; }
}

update: I changed AddColor controller code.I also tyr to add ColorDB color = new ColorDB(); and color.Color = "testColor";The value can insert to db but ColorDB colalso null.The problem seems to Mvc Controller can't Receive ajax data.

public string AddColor(ColorDB col)
        {
            ColorDB color = new ColorDB();
            color.Color = "testColor";
            if (color != null)
                {
                    db.ColorDB.Add(color);
                    db.SaveChanges();
                    return "add success";
                }
                else
                {
                    return "add fail";
                }
            }