The key to painting a white flower is to keep it simple. Don’t overdo it! There’s usually a sufficient amount of pigment in the wash bucket to break up the stark white of the paper; you may only have to add a little bit of color to imply the petal’s shape. Another general rule is to work in this sequence: Apply water and then color.
1. I drew the flowers in pencil on a sheet of Arches 300-lb, cold-pressed paper. Using a No. 30 brush, working one petal at a time, I applied water almost to the pencil line. The leftover color in the water of the wash bucket was enough to break up the stark white of the paper.
2. After water is applied using a # 8 nylon synthetic brush apply just a little color (Naples yellow with a touch of perm. Quin. magenta) to the base of the flower and pull out to the edge of the petal. repeat a few lines using a shadow blend of French Ultramarine blue and Burnt sienna mix. The leftover color in the water of the wash bucket was enough to break up the stark white of the paper.
3. Once I’d made sure each flower had a shape, I picked up a No. 20 round (a blend of natural and synthetic fibers) to start adding shadows with a mixture of French ultramarine blue and burnt umber.
4. Next I worked on values. I changed the values slightly each time I painted a shadow: a darker color toward the bottom, a lighter value toward the tip5. The shadows make all the difference, as they define the flowers and convey the effect of transparency. To keep these areas from looking flat, I varied the areas of dark and light as I worked.6. Adding stems will add more color and help ground the painting. As I did with the flowers, I applied water first, then the color. For this green, I mixed permanent sap green and French ultramarine blue; I used a No. 8 to apply color to the outside edge of the stem. Then I allowed the color to run back into the center. To make the stem more interesting, I applied a stroke of quinacridone magenta along one side.
8. For the background, I used my No. 30 brush and a wet-into-wet technique to help pull color into areas and to remove unwanted lines.
You can find more step-by-step demonstrations and information in my book "Watercolor in Motion"