I really like to teach at least one color lesson per grade level. For third grade I always create a lesson on value. This lesson I found on http://kids-finelines.blogspot.com/2010/10/ghost-eye-tree.html. It it great for this time of year. It is based on the story "Ghost Eye Tree" by Bill Martin. I actually read the entire book to my third graders, but had to replace certain words like stupid and dumb with silly and crazy.
The first day I read the story and then we experimented with color. I gave each table a palette of blue and white. Students painted a circle white for the moon first.
Then I added blue to the white students mixed to create a light tint. This tint went around the moon.
Next more blue was added to make a darker tint. This went around the moon again.
The original "True" blue was added around and around the moon after the tints.
For the first shade I added a little black to the blue in the palette. Students mixed. This was painted next.
Finally I added more black to make the blue the darkest shade. This was used on the rest of the paper.
On the second day we created the tree with black construction paper. I actually have no photos for this step. You can follow the above blog for more directions on how to teach the tree.