Select plants you wish to use as paint colors. For example, you can use beets (red), cayenne pepper (rust), yellow onions (yellow and orange), Queen Anne's Lace (green), blueberries (blue or purple) and orange pekoe (brown). Chop the selected plants into small pieces and set aside in separate bowls.
Spoon the first plant matter into the pot. Add double the water to the plant material. Simmer the mixture for approximately one hour, stirring occasionally. Remove from the stove and cool.
Place the strainer on the jar. Pour the mixture slowly into the strainer. Gently press the pulpy mass to release extra color. Wipe any spilled fluid on the sides of the jar with paper towels.
With each color you make, dip your paintbrush into the jar and paint a small line on watercolor paper. Next to the line, document the color and plant material, describing the volume of plant matter used.
Cover the jar with a lid. Mark the plant matter and color onto a label and stick it on the corresponding jar. Store until ready to use. Natural watercolors will evaporate over time. Simply add water to the consistency you desire to continue enjoying your watercolor paints.