To make, use a pencil to lightly trace a leaf onto good-quality watercolor paper, then gently erase the outline so it’s barely visible. Dip a paintbrush in plain water and carefully fill in and saturate the leaf shape, making sure not to exceed the outline. Working quickly, dip the brush in watercolor paint and very delicately touch it to the wet shape in a few places; repeat with other colors as desired. The pigment will fill in the shape.
SOURCE:http://www.marthastewart.com/1083266/turn-over-new-leaf-watercolor