In the bowl of an electric mixer fitted with the paddle attachment, beat together cream cheese and butter on medium speed until mixture is light and fluffy, about 3 minutes. Scrape down bowl with a spatula. Add creme de cassis, food coloring, and salt; mix on low for 30 seconds.
With the mixer on low, slowly add 2 1/2 cups confectioners' sugar; beat for 30 seconds. Scrape down bowl. If consistency is too soft to hold its shape, add additional confectioners' sugar, 1 tablespoon at a time, until desired consistency is reached.
Cassis filling can be kept refrigerated, in an airtight container with plastic wrap pressed on the surface, for up to 5 days.