In a large mixing bowl, mix together the cream cheese, sour cream, sugar, and vanilla until well combined. Add both kinds of grapes and mix well.
If desired, transfer the grape mixture to a serving dish. Cover and refrigerate until serving time, at least 2 hours.
Just before serving, sprinkle brown sugar and pecans over the top.
Notes
It’s best to make this just the day before serving at the very most, otherwise, the grapes will soften too much and leave a poor texture! This salad does, however, taste best when it’s chilled, so do leave some prep time that. Ideally, you should try keeping it in the fridge for 2-3 hours before you’re ready to serve. Toppings like brown sugar and pecans should be placed just right before serving, though.
Skinning the grapes isn’t necessary at all, although I recommend it if you’re serving the salad to little ones to cut the grapes into smaller pieces.