Preheat the oven to 275 degrees F. Line 2 baking sheets with parchment paper. Put the egg whites and the salt into a large clean bowl, and whisk until soft peaks form. Gradually add the sugar, 1 tablespoon at a time, whisking between each addition, until it has all been added, and the meringue is satiny and forms stiff peaks when the whisk is lifted from the mixture. Using a large metal spoon, fold in the vanilla extract. Using a piping bag fitted with a 5/8-inch tip or alternatively a spoon, pipe or scoop the mixture into individual meringue approximately 2 3/4-inch wide onto the prepared baking trays. To achieve the ripple color effect, dip a wooden or metal skewer into your chosen food coloring and swirl it through each meringue. Bake in the oven for 30 minutes. Test one by lifting and gently pressing on the base of a meringue. They should be crisp but give way with a bit of pressure. They will crisp more when cooling. Turn off the oven, and let cool in the oven, with the oven door slightly ajar for best results. If possible, allow them to cool completely in the oven.
To make the cream: Place the raspberries and sugar in a food processor, and whiz or pulse, until smooth. Push the mixture through a sieve into a bowl to remove the seeds. Fold as much puree as you wish through the whipped cream, leaving it rippled or streaked, if you like. Place a generous tablespoon of the raspberry cream on one half of the meringue and sandwich together with another meringue. Serve any remaining puree on the side.
The meringues will keep for 2 or 3 days in an airtight container unfilled, but need to be eaten within half an hour once they have been filled.