I just got a new book which I think is fabulous! It's Painting and Drawing in Waldorf Schools: Classes 1-8 by Thomas Wildgruber.
There's a helpful amount of theory but also LOTS of full color pictures of student work. Introduction, a chapter on form drawing, a chapter on free versus guided drawing (including how the alphabet is introduced pictorially), and chalkboard drawings. A chapter on playing with paint versus guided painting.
Then, the school years.
A large section on each grade, with a series of assignments (and photos of student work) for each grade up to grade 8. He talks about the painting and drawing work separately, as its own subject, as well as how it ties in with each main lesson, and examples of assignments and student work. There are considerations and notes for each assignment.
You can get the book through Amazon. I think it's a great all-in-one resource that would be really helpful!
I would also like to say that not all Waldorf painting books agree. I read years ago that you should mix the two yellows (lemon and golden) that you get from Stockmar to make one "true" yellow, and the same with the two reds and the two blues.
That is for the early grades. Then, later on (I believe it was fourth grade, Norse mythology) you would allow for students to compare and contrast and work with the different shades. My mind is vaguely recalling that this is in Painting in Waldorf Education? My book is at school so I can't look it up right now, but I remember something about Norse creation and the two reds. Feel free to correct me if I'm referencing this wrong.
Anyway, the Wildgruber book allows the children to work with both yellows, blues, and reds almost from the beginning and my students are so excited to see and compare the two colors of each. They are absolutely absorbed by the differences. So that has been really compelling for them. We got the paint jars and wooden holders from A Child's Dream Come True and Nova Natural. I prefer the Nova Natural one; it's larger and has larger jars. It also has lovelier lines. But they both work perfectly fine. And the children love (as I said) the variety of colors. They look quite beautiful on the tables.