Combine powdered sugar, salt, cream, and vanilla in the bowl of a stand mixer fitted with a paddle attachment. Mix at low speed to moisten, then increase speed to medium and beat until creamy and soft, about 5 minutes. Using a spatula, scrape frosting into a small bowl, or as many bowls as you would like colors, and cover with plastic pressed directly against the surface. Set aside until needed, up to 24 hours at room temperature.
