Prepare sugar-cookie dough, adding several drops of yellow food coloring, and refrigerate 1 hour.
Heat oven to 350°F. Shape heaping tablespoons of dough into balls. Using your hands, roll each ball into an 8 inch-long rope. Form each rope into a circle, pressing ends together. Arrange cookies 10 apart on baking sheets. Brush each circle with corn syrup, and sprinkle with yellow sugar crystals.
Bake cookies until golden, about 20 minutes. Transfer to wire rack and cool.
Using icing, attach candies to make jeweled rings.
In large bowl, with electric mixer on low, beat together powdered sugar, powdered egg whites, water, and cream of tartar until well combined. Increase speed to high, and continue beating until stiff peaks form. If not using immediately, press piece of plastic wrap directly onto surface of icing and store in refrigerator for up to 1 week. Bring icing to room temperature before using.