I tried my hand at a new-to-me cake decorating technique for a cake I made for my grandmother's 90th birthday party this weekend, and loved the result! I was inspired by pen and ink drawings of wildflowers my aunt had done and wanted to bring them to life on this cake.
I used food markers and food coloring gel to achieve a hand-painted effect. Using a very light hand, I used a black food-safe marker to sketch out the entire design on the fondant before adding the color. Working with food gel is not unlike watercolor paints. Just squeeze a small amount of gel, or if it's in a pot, use a toothpick to put a small amount of gel onto your palette, lightly wet your brush, and start adding color to your design. Be careful not to get your brush too wet, especially on vertical portions of the cake so that you don't have water running down the sides. Food paste/gel is much more concentrated than regular food coloring, so the color payoff is much more vibrant and easier to achieve your desired effect.
Fondant is more forgiving than paper; if you make a mistake, use a clean brush and fresh water to dilute what you want to remove and dab with a paper towel. Let that area of fondant dry before going back in with new color. Change your water frequently, or anytime you start to work with a new color.