I always keep a variety of brushes on hand when decorating. They are great for painting on color, applying luster, pearl, or petal dusts, applying an edible glue, or gently adjusting decorative accents and details.
(via Amazon) The Wilton 5-Pc. Decorating Brush Set makes it easy to learn to paint cookies, cakes and cupcakes with designs from impressionistic to detailed--- Soft, synthetic bristles are food-safe for all decorating applications--- Use the liner brush for details, the round brush for thin or thick lines and the small flat brush to shade and blend colors or for brush embroidery--- Paint curved strokes or flower petals with the angled flat brush and go bold with designs or lines with the large flat brush--- Before first and after each use, hand wash with warm water and gentle soap. Squeeze excess water. Reshape brush. Air dry thoroughly. Made in China