In a mixing bowl, use an electric mixer to beat the room temperature cream cheese until smooth and creamy.
Gradually add the granulated sugar and continue mixing until fully incorporated. Then, add the pure vanilla extract and sour cream, mixing until smooth.
Gently fold in the washed and dried red and green grapes without crushing them.
Sprinkle in the light brown sugar and the chopped pecans, if using, and fold until evenly distributed.
Cover the salad with plastic wrap and refrigerate for at least an hour before serving.
