Place the water and erythritol in a small sauce pan and heat over medium until the erythritol has dissolved, stirring occasionally. This should only take about 2-3 minutes.
Remove the pan from the heat and whisk in the gelatin to dissolve completely.
Place the softened cream cheese and vanilla extract in a medium bowl or the bowl of a stand mixer.
Add the gelatin mix to the bowl with the cream cheese and beat until completely smooth and slightly fluffy.
Divide the cream cheese mixture into three, equal parts.
Stir in the pureed blueberries into 1/3 of the cream cheese mix and then add the pureed raspberries to another 1/3 of the mix. This will give you a red, blue and white mousse.
Scoop some of the raspberry mousse into four small clear glasses.
Top the red mousse with the white mousse then top each with the blue mousse. You can use a piping bag to make the mousse even more beautiful!
Place the mousse cups into the fridge to set for about 2-3 hours. Serve chilled.