In a large bowl, mix powdered sugar, milk and extract until smooth. Add additional milk if necessary to make icing thinner. Spread icing toward edge of cookie, leaving a 1/4-inch border uncovered. Use the decorating gels to decorate cookies with stripes, dots or streaks of color. Add the decorating gels while white icing is wet for a blended look, or allow white icing to dry before decorating for vibrant colors. To create the cobweb look, make lines or circles on the cookies with the decorating gels while the white icing is still wet. Run a toothpick crosswise through the colored lines to make designs.