In a small bowl, whisk the flour, baking powder and salt. In a large bowl, using an electric mixer on medium, beat the sugar and butter until light and fluffy, stopping occasionally to scrape down the sides of the bowl, about 2 minutes. Add the egg and the orange zest and juice. Beat on low until blended, stopping occasionally to scrape down the sides of the bowl, about 1 minute. Add the dry ingredients; beat on low just to blend. Cover and chill 1 hour. Transfer the dough to a sheet of parchment or wax paper; form into a 1 1/2-inch-diameter log. Roll in colored sugar, then roll in the paper and freeze until firm, at least 2 hours.
Position racks in the top and bottom thirds of the oven; preheat to 400 degrees . Unwrap the dough and cut into 1/4-inch-thick slices. Divide between two nonstick or parchment-lined baking sheets, spacing 1 inch apart. Bake until golden brown around the edges, rotating sheets and reversing from top to bottom halfway through baking, 8 to 10 minutes. Transfer the cookies to a wire rack; let cool. Repeat with remaining dough on clean, cold baking sheets.
