I received an email recently from someone who had visited my website and blog, asking me about the techniques I used to fill in the color on some of my party cakes, specifically the cakes shown on this post. Thanks to Julie for her question.
After pressing the pattern into the buttercream frosting, I outline the pattern with a normal consistency buttercream. To make the flow-in color, I add liquid paste color to the buttercream, and then thin it with Karo corn syrup. Using writing tips, I flow it into the the outlined pattern.