Dissolve the red Jell-O in 1 cup boiling water. Stir until fully dissolved, then add 1 cup cold water. Pour about ⅓ cup into each cup to form the first layer. Refrigerate until set, about 1 hour.
Once red layer is firm, spoon in 2–3 tablespoons of whipped topping to form the white layer. Smooth gently with a spoon. Return to fridge for 15–30 minutes.
In a separate bowl, dissolve the blue Jell-O in 1 cup boiling water. Stir in 1 cup cold water. Let it cool to room temperature (important!).
Pour about ⅓ cup of the blue Jell-O gently over the whipped topping layer. Chill again for 1–2 hours, or until fully set.
Top each parfait with a swirl of whipped cream, a few blueberries, and a sliced strawberry. Serve chilled.