In the bowl of a stand mixer fitted with the paddle attachment, beat butter until creamy. Gradually add 1/2 cup of confectioners’ sugar and 1/4 teaspoon lemonade Kool-aid powder. Beat on medium-high speed until light and fluffy. Mix in the lemon juice, zest, and salt. With the mixer speed on low, add the flour in three additions, mixing until incorporated and scraping down the bowl after each addition.