Prepare the Cookies: Beat butter and powdered sugar with a stand mixer fitted with a paddle attachment on medium speed until light and fluffy, about 2 minutes. Add vanilla, and beat until combined, 20 seconds. Add flour and salt; beat on low speed until a smooth dough forms, about 2 minutes.

Transfer dough to a lightly floured work surface; shape into an 8-inch-long x 2-inch-wide log. Wrap with plastic wrap; chill until firm, at least 2 hours or up to 2 days.

Preheat oven to 350°F. Line 2 baking sheets with parchment paper. Remove dough from refrigerator; unwrap. Slice into 24 (⅓-inch-thick) rounds. Arrange 2 inches apart on baking sheets. Bake in 2 batches until edges are golden, 11 to 12 minutes per batch. Cool on baking sheets 5 minutes. Transfer to a wire rack; cool completely, about 20 minutes.

Prepare the Royal Icing: Place powdered sugar, meringue powder, and 6 tablespoons warm water in bowl of stand mixer fitted with a whisk attachment. Beat on medium speed until fully combined and smooth, about 1 minute, stopping to scrape down sides of bowl as needed. Increase mixer speed to high; beat until icing is no longer glossy, about 1 minute. Stir in more warm water, 1 tablespoon at a time, until a spreadable consistency is reached. Spoon mixture into a piping bag or a ziplock plastic bag with 1 corner snipped off. 

Pipe Royal Icing onto Cookies, using a wooden pick to fill and spread to edges of each. Let stand at room temperature until dry, 1 hour.

Squeeze a few drops of assorted food coloring into separate small bowls. Add 2 teaspoons almond extract to each color, and stir with a small paintbrush. To test your colors, paint a few practice strokes on a paper towel. (Add more extract if you want the colors to be lighter.) Paint Cookies. Dry completely, about 1 hour.