This lesson is a little more than beginner level, but if you have done some shading in the past you should be able to do this lesson just fine.
Tinting the background is optional and you would have to wait for it to dry, but a very pale, pastel, lavender hue is pleasing on the final product. Add just a touch of color to a dollop of white. Mix well if you want a consistent color, less well if you want a bit of variation in the background. Let the canvas dry completely.
With yellow paint on a large or medium round brush, paint a stem for the main iris and the iris bud. Mix french blue and yellow (medium green to light green).
Using same brush, paint along the left side of the yellow stems creating a shadow. Be sure to leave some yellow on the sunny side of the stem.
Once you have establish the foundation colors of your large iris, take a small, round brush with green to create leaves at the base of the large iris.
Use magenta or red with white to mix a dark pink, a medium pink, and a light pink.
To draw in your largest iris flower, use your lightest pink to shape your flower.
Use a variety of pink values (different shades of pink; dark, medium, light) to add movement and depth to iris flower.
Working a pattern so that the flower touches the top of the green stem on the lower part of the iris nearest the stem, use strokes moving from up top to the bottom to create lines where there might be lines in an upside down fan shape.
Paint the other iris buds and add a darker pink to violet to shade the left side (as with the stem).
With medium pink, create more detail in the shape of the foreground iris petals.
Add the dark side of the other flower petals.
Now mix french blue and magenta or red to create a violet. Mix 3 values; dark, medium, light.
Darkest violet should be a deep blue-violet for the shadow side of the iris bud. [Click on image to enlarge for detail]
Use darkest pink magenta or red to create the shadow on the left side of the iris petal.
Use dark violet in large iris to create veins across the middle back petal.
Add in medium to dark pink for variation and to soften. Add pink tip to small center bud, and add more violet and dark pink to iris flower to create folds.
With yellow, add yellow fluffies to the side/center of top petals, in two places.
[Click on image to enlarge for detail]
Experiment with adding detail. Do no feel the need to copy my example. As each flower in nature is different, so each painting of an iris should be unique. Make it your own, and then…
Sign your work.
Always learning, always improving!